Septic tank size requirement FAQs.

This article series provides septic tank size tables to determine the required size or capacity of a septic tank, and it explains how to calculate septic tank volume based on septic tank inside dimensions measured in feet, and we discuss the sizing, installation, and functions of septic tank tees to prevent septic system clogging.

FAQs about Septic Tank Size Calculations & Requirements

These questions & answers about septic tank sizing or size calculations were posted originally at SEPTIC TANK SIZE - home. You will want to see the tank capacity or sizing tables and guidelines given there.

Also see more-recent questions about septic tank size or capacity at SEPTIC TANK SIZE FAQs-2

How big does our septic tank need to be? Typically the septic tank volume for a conventional tank and onsite effluent disposal system (such as a drainfield) is estimated at a minimum of 1000 gallons or 1.5 x average total daily wastewater flow.

On 2018-07-12 - by (mod) - how does 2 -1200 gallon septic tanks with a 1000 gallon lift pump chamber work?

Chad:

I can only offer a general answer since I have no details about your septic system.

Black water (sewage toilet water and probably all other wastewater) from your new house flows into septic tank #1.

In Tank #1 provided the tank is properly sized for the house's wastewater flow rate/volume, and provided that the tank is properly maintained (pumped on schedule to avoid clogging the tank with solid waste), the wastewater separates into floating scum and settled sludge, and some bacterial action begins to break down sewage and pathogens.

Because septic tanks are normally always full, whenever wastewater flows into tank #1 it pushes an identical volume of water out into tank #2.

Baffles at Tank #1 outlet block the floating scum/solids, keeping them in tank #1 while permitting clarified effluent-wastewater effluent to flow into septic tank #2.

In Tank #2 further separation of solids and settlement occurs.

Wastewater flowing into Tank #2 pushes further-clarified effluent out into the pumping chamber.

When the liquid level in the pumping chamber rises sufficiently near the chamber top, a float-activated switch turns on a lift pump.

The lift pump moves clarified effluent out of the tank into a soil absorption system, aka drainfield, leachfield, soakaway, or soakbed, depending on where you live and local terminology.

In the drainfield effluent soaks into the soil where further bacterial action processes its pathogens to avoid contaminating the environment.

Above at INDEX to RELATED ARTICLES: ARTICLE INDEX to SEPTIC SYSTEMS you'll see a complete list of septic system articles including SEPTIC TANK PUMPING SCHEDULE that you should review.

On 2018-07-12 by Chad D

We move into our new house in a week, we are going from city sewer to a septic system. I just received the test reports and all is good, my question is how does 2 -1200 gallon septic tanks with a 1000 gallon lift pump chamber work?

On 2017-09-08 - by (mod) - Shared septic systems for 30 homes

Steve

Shared septic systems would, in my opinion, fall under community septic system regulations.

There is almost no chance that a conventional septic tank and drainfield would support 30 2 bedroom cabins - potentially 120 people at maximum daily use. You'd need a small onsite wastewater treatment plant.

Only if you could establish a much smaller maximum simultaneous usage might it be reasonable for the local health or building code officials approve something different. Typically a septic system is designed for the maximum use that could be made of it.

So for example a couple building a new four bedroom house would not be successful in arguing to the local code approvers that only two of them would live in the house. An astute code official would reply "yes but the home is designed with four bedrooms; the septic for that home has to be able to handle the people who could be in the home, including guests or the larger family of a future owner.

On 2017-09-07 by Steve

Are there special standards for shared septic systems in a seasonal community (May to September).

Could a single centrally located conventional septic system support 30 2 bedroom, 1 bath cabins? Alternatives?

On 2017-06-22 - by (mod) - What size septic tank will we need.. 2 adults

Rosemary.

At hSEPTIC TANK SIZE TABLES

You'll find a septic tank size guide

On 2017-06-21 by Rosemary

We have built a 1 bedroom 1 tiny bath in our small cabin.
In Texas. What size septic tank will we need.. 2 adult. People will
Occupy the place.

On 2019-05-28 by (mod) -

Have you asked your building department if they have kept records of Prior code requirements?

On 2019-05-23 by Sheila

How would I find out what requirements were in effect in Yavapai County AZ in 1982 regarding septic tank sizing?

On 2019-02-01 19:42:31.090320 by (mod) -

Michael

That's how it appears to me, except for cases of very little wastewater volume;

The case you describe, in extreme is called concentrated wastewater, for which there has been research. Examples:

De Graaff, Marthe S., Hardy Temmink, Grietje Zeeman, and Cees JN Buisman. "Anaerobic treatment of concentrated black water in a UASB reactor at a short HRT." Water 2, no. 1 (2010): 101-119.

Luostarinen, Sari A., and Jukka A. Rintala. "Anaerobic on-site treatment of black water and dairy parlour wastewater in UASB-septic tanks at low temperatures." Water Research 39, no. 2-3 (2005): 436-448.

Gray, N. F. "The influence of sludge accumulation rate on septic tank design." Environmental Technology 16, no. 8 (1995): 795-800.

The point of articles like the last one is we need sufficient water volume for settlement time and treatment, and to avoid blocking the tank or clogging it to the point that wastewater can't flow through it and effluent out to the drainfield.

On 2019-02-01 by Michael

Again, thanks Dan. Bottom line, black water septic tank design is the same as comingled. Got it.

On 2019-01-31 by (mod) -

Michael:

Typical design-retention time for septic tanks is 1-3 days in some sources or better, 2-3 days but there is not a single exact answer since tank sizes and shapes vary. The formula below gives a reasonable septic tank effluent retention time in days based on the tank volume and daily wastewater volume.

Details are at our article on EFFLUENT RETENTION TIME

On 2019-01-31 by Michael

Thanks Dan. Then a standard 2day+/- septic tank retention time should provide sufficient process time?

On 2019-01-31 by (mod) -

Michael

I think you'd use a conventional tank and drainfield if your site has space and usable soils. With a 2 gallon flush volume there ought to be sufficient water for the tank and fields to operate. The modest total wastewater volume probably means that if your soils have decent perc you won't need much total area.

On 2019-01-30 by Michael

I'm an engineer volunteering with an NGO to design, and construct sanitation facilities for African primary, and secondary schools. There is a current proposed black water only septic system project. How do you design/size a black water only septic tank? The only influent water will be approximately 2gal/flush.

On 2018-12-21 by (mod) -

The table in the article SEPTIC TANK SIZE

Table of Required Septic Tank Size Based on Daily Waste-Water Volume in Gallons

Maps septic tank typical waste water flow to gallons of tank dize

On 2018-12-20 by Alan

Can't figure it, what is the answer in gallon capacity

On 2018-10-20 by (mod) -

You will need an on-site wastewater treatment system, Thulani. A conventional septic tank and drainfield would have to be larger than you are likely to be able to accomodate.

On 2018-10-20 by Thulani M Ndlovu

I would like to build a septic tank to accomodate to 96 people(48) bedroom.I bought a (10000sqm) plot in order to build rented houses.
Kind regards
Thulani
Contact no 0609633554
email mlumax75@gmail.com

On 2017-05-25 by (mod) - Re: options for treatment of urine & water wastewater systems

Emile:

Regarding your question of treatment of urine and water mixture, I can't answer without knowing the intended application.

Normally urine and other wastewater flows either into a public sewer and on to a sewage treatment plant or into a private septic system where the wastewater in a conventional system is treated by bacteria in the septic tank (45%) and by both aerobic and anaerobic bacteria in the soil of the soakaway bed (55%).

Aerobic septics and other designs treat wastewater to different levels at different states of the process. Still other systems may use a disinfection step combining UV light or chlorine injection.

On 2017-05-25 by emile

what are the best technologies to treat urine and water mixture?
thank you

On 2017-05-09 by (mod) re: what's the size of a 1250 gallon septic tank?

Deric

From the table at SEPTIC TANK SIZE

1200 gallon: 111 x 78 x 61inches for the tank plus a couple of feet on sides for placing the tank and for making piping connections

On 2017-05-09 by Deric

What is the size of the hole for a 1250 gallon septic tank

On 2017-04-06 by (mod)

Tony

Typically the sizing of a septic system involves BOTH the tank capacity AND the area and capacity of the drainfield. Just adding a tank won't address the second half: how to dispose of effluent. The system, to avoid a failure and contamination, has to be able to handle the maximum daily wastewater inflow.

But indeed I'd look at extending the existing system before installing a whole new one.

On 2017-04-06 by Tony

I am planning to build a house. 1800-2000 sq. feet. with 2.5 baths room. The vast majority (95%) of the time it will only be my wife and myself (2 people). We also already have a small building. Living space 400 sq. ft. No one would live there. only for occasional guest. It has 1 bath. so total 3.5 baths. 2 people 95% of time.

I already have a 1,000 gallon septic system system consisting of two 500 gallon tanks. two drain field lines each being 67 feet in length. According to the septic report the soil type is 3. If by chance the county comes back and tells us the system is to small,,, can we just add one additional 500 gallon tank to increase the volume instead of installing a totally new system. If not, would it be cheaper to install a separate system for either the house of the small building? thanks for any help you can provide.

On 2017-03-16 by (mod)

Cheryl, as you'll read in the article at SEPTIC TANK SIZE septic tank size is not a function of house square feet, but rather it depends on the number of occupants, bathrooms, volume of wastewater to be produced, and probably, depending on where you live, a minimum septic tank size specified by local codes and ordinances.

On 2017-03-16 by Cheryl parker

Im building a 980 square foot tiny house. What is the requirement size septic tank

On 2017-01-20 by (mod)

Pavan,

Depending on occupancy and level of wastewater use you may need to install an onsite mini-wastewater treatment facility since a conventional home-type septic tank and drainfield may not be adequate.

The question is not just septic tank size but the size, design, layout of the effluent absorption field. I'd consult a local septic who also can take into consideration the properties of the soil where your facility is located, site shape, layout, slope, available space, and local codes and restrictions.

On 2017-01-20 by pavan

We have a working staff of 30 members,how much capacity of septic tank is preferred for us,
pavan301030@gmail.com

We have a industry, working staff - 30 no.s, how much capacity of septic tank is required for our use.

On 2017-01-20 by (mod) - septic tank size for 30 employees

Pavan,

Depending on occupancy and level of wastewater use you may need to install an onsite mini-wastewater treatment facility since a conventional home-type septic tank and drainfield may not be adequate.

The question is not just septic tank size but the size, design, layout of the effluent absorption field. I'd consult a local septic who also can take into consideration the properties of the soil where your facility is located, site shape, layout, slope, available space, and local codes and restrictions.

On 2017-01-20 by pavan

We have a working staff of 30 members,how much capacity of septic tank is preferred for us,
pavan301030@gmail.com
We have a industry, working staff - 30 no.s, how much capacity of septic tank is required for our use.

On 2016-12-20 by Daniel

Hi,
I just purchased 75 acres of heavily wood ,predominantly level property in Maine. My plan is design & build 220 r/v-campsites. Phase one of four will break ground may/2017 and calls for the installation of 55 individual campsites with water power & waste hookup.

My question is it feasable or possible to install one large downstream septic & field instead of individual designs for each site..my calculations indicate the measurements will be 250 x 400 x 10.5 deep (inside measurements) plastic/fibreglass tank.

I know its possible but will it pass Title-V regs. I have experience in the construction trades and know individual inspectors can be tough..what ya thoughts

On 2016-11-15 by akbruce

Azmat al i- You don't design a tank, you buy a tank. You design a system, but usually that is required to be done by an engineer. The fact that you are asking how to do it illustrates why that is the case (plus you couldn't build one as cheaply as buying one).

On 2016-11-11 by Anonymous

Drawing for 7ft. Deep ×6 with.×9ft lenth

On 2016-10-13 by Azmat ali

How to design a septic tank

On 2016-10-05 by Rosa

Question?? What size tank and number of gallon capacity is needed for a duplex consisting of 2 units occupied by 1 person each ??

On 2016-07-04 by (mod) - septic tank grandfathering rules

Will, the "grandfathering" clause in some buliding codes is a local policy not somehting one an answer about an unknown property at an un-known location, city, state or Province, and country.

However I can speculate that as in concept "grandfathering" pertains to structures that were already-built before current applical building codes, an d as your third bedroom did not then and does not yet exist, I would expect local officials to say no.

Besides, building standards describe a minimum not a maximum performance level. In fact you most-likley want your septic system to work properly, have a long life and to avoid discharging sewage into the groundwater or environment. That means to me that your tank is too small in absolute terms.

That in turn means that it won't treat the volumeof seweage adequately and that you'd be asking for trouble in the form of more rapid failure of the drainfield or sewage in your well water.

On 2016-07-04 by Will

20 yrs ago a larger than needed septic tank was installed with a future intent of adding a 3rd bedroom.So they installed a 750 gal. Tank back then.

Now 20 yrs later it appears the cnty. Health dept may require a 1000 gal tank. Is it possible that i could be grandfathered in since due dillagence was established 20 yrs ago just in case we add a bedroom?

On 2016-06-24 by (mod) re: how many openings are there in the top of a septi ctank?

Usually there are openings at both ends of all septic tanks - as one needs to be able to inspect or repair both inlet and outlet baffles;

Some septic tanks such as older round steel tanks had a single removable cover over the whole tank;

Other septic tanks, particularly larger ones will have three or more openings including inlet end, outlet end, and center compartment, and a septic tank with more than three compartments will have additional openings for inspection or cleaning.

An aerobic septic tank will have an opening over the inlet, the aerator and aeration chamber, over any settling chambers.

Other septic tank systems will sport openings over an additional pumping chamber if one is used to lift effluent to a raised elevation, raised bed or mound system.

When your tank is pumped your pumper can use a light and mirror to make at least a limited inspection of the tank interior.

On 2016-06-23 by Duke Of Hudson

"CONTINUED":used to lift a square opening. Do you think this is the only opening used for pumping this size septic tank,or do I need to remove" all the soil" from the top of the tank to be sure? I don't know any history for this septic tank!

I'm planning on having my septic tank pumped(emptied). The top of the septic tank is aprox. 9ft. X 4ft.,I've located one opening,towards one end of the tank. I've dug across the center,from one end to the other end,there's a "metal hoop on one end that's bent over" and doesn't appear to be an opening,the other end of the tank has a metal hoop also & is obviously

On 2016-04-12 by (mod) - septic tank size capable of handling an added bedroom?

Victoria:

You need the septic system design, tank details, field details, site plan, and then you'll need to review that with your local building department and perhaps a septic engineer.

You should discuss with your lawyer the ethics as well as legal exposure of listing as a 4-bedroom home a property approved for only 3 bedrooms as well as the question of what was disclosed to you or represented to you when you purchased the home.

On 2016-04-12 by Victoria

We purchased a new 4 bedroom home last year. We have recently found out that the septic system was done for a 3 bedroom home and is listed with the county as a 3 bedroom home. Is there a way to have our current septic system re-classified or approved for our 4 bedroom home?

All of our real estate listings, floor plans, etc., that were given to us when we purchased the home say it's 4 bedrooms. The 4th bedroom has a closet, walk-in as a matter of fact and a window for escape in case of a fire.

We know that listing our home for resale as a 3 bedroom home versus a 4 bedroom home will decrease our value and we feel mislead by the builder and the realtor representing the builder. Do you have any suggestions or do we have any recourse? Thank you!

On 2016-03-23 by (mod) - does number of bathrooms determine septic tank size?

Good question, Kent.

I have not found a table converting "number of bathrooms" to septic tank size. Even "bathroom" is unclear since more water will be used in a full bath than in a half bath or a water closet alone.

Here is the Kansas septic design guide

http://www.kdheks.gov/nps/resources/mf2214.pdf

In that Kansas septic design guide at table 7 you'll see that Kansas uses number of bedrooms, as we discuss below.

This link http://www.kdheks.gov/nps/lepp/ provides other Kansas guides for septic & graywater systems.

For that matter, one person might live in a one-bedroom, 3 bath home.

That's probably why other common tables for guesstimating septic tank size estimate daily wastewater flow by guessing at number of occupants - in turn some tables guess at number of occupants by specifying the number of bedrooms.

Ask your local building department if they have a reference or citation and please use our page bottom CONTACT link to send me that information - what we learn will help other readers.

On 2016-03-22 by Kent

I've been told that if I buy a house in Saline County, Kansas, the size of the septic tank is determined by the number of bathrooms in the house. All I have been seeing is water flow in gallons per day to determine the size of the tank. Any help or suggestions where to find the correct answer?

On 2016-02-23 by (mod) re: tank dimensions don't come out to the exact volumes quoted for those "sizes"

Thanks QG you make an excellent point.

For example septic tank dimensions and capacities I copied actual septic tank dimensions from several manufacturers as well as their rated or nominal tank sizes for those dimensions.

Keep in mind that outside dimensions of a tank are going to be larger than inside dimensions, varying depending on the tank wall thickness - for concrete tanks or site-built masonry tanks. (Metal and plastic or fiberglass tanks have such thin walls that the OD vs ID distinction is not important).

Nominal septic tank actual internal volume or "size" is therefore not the same as exact external volume, with a greater difference between those if a tank is thick-walled concrete than if it is thin-walled plastic or fiberglass.

Nominals septic tank capacity will be different (and less than) the actual internal volume of the tank because a septic tank in proper operation is filled only to the bottom of the tank outlet pipe, never to the tank top.

On 2016-02-23 by QestionGuy

The tank sizes by dimension do not come out to be the tank size (in gallons) listed. For instance, the tank dimensions for a 2000 gal tank are 162" x 78" x 64", which comes out to be 468 cf, or 3500 gal.

On 2016-01-27 by Wendy

How many bedrooms can a 1,000gal 2 chamber tank accomidate in Washington State???

On 2015-12-15 by (mod) - designing a septic system for 1200 people

Anon:

If you are designing an onsite waste disposal system for a facility housing 1,200 people, a conventional residential septic tank such as those shown in the tables at

SEPTIC TANK SIZE would never be adequate. More likely you'll need an on-site wastewater treatment plant designed by a sanitary engineer.

The engineer will consider daily wastewater flow and will also consider the physical size of your building site and where you can locate both treatment facility and effluent or wastewater disposal facility.

On 2015-12-15 by Anonymous

How to calculate the size of a septic tank for 1200 persons

On 2015-11-06 by (mod) -

There is not a standard distance, How, but typically the dimensions of a pre-cast concrete tank of 1000 gallons are 10 ft. x 5 ft. so you can figure that the openings at the tank inlet and oulet will be less than 10 ft. apart.

On 2015-11-06 by How far apart are the holes (2) on a iooo gal septic tank

How far apart are the holes(2) on a 1000 gal tank

On 2015-10-05 by Richard

What would be the right size tank for a small (80 sq. ft.) pool house?

On 2015-09-06 by (mod) -

For a large commercial system such as a 300 person event hall you need help from a septic engineer as wel as more data that she will askmyour to help estimate, such as frequency of hall use and length of use. I estimate you may need a 15,000 gallon septic tank and a drainfield capable of handling surges of wastewater volume exceeding 40,000 gallons per day. You need to include all wastewater sources not just visitors, such as kitchen activity and staff.

Please see COMMERCIAL SEPTIC DESIGN -https://inspectapedia.com/septic/Commercial_Septics.php

On 2015-09-06 by Tony

How big of a tank would you need to accommodate a 300 seat wedding hall

On 2015-07-29 by Salvador Barona

How to compute size of septic tank based on the number of occupants.

On 2015-05-13 by (mod) -

Anon:

Start by obtaining a septic tank size based on the tables in the article above. Typically, Canadian or British Columbia codes will agree with the septic tank sizing tables above. Then check with your local building or health department to determine if they have other requirements.

On 2015-05-13 by (mod) -

Anon:

start by obtaining a septic tank size based on the tables in the article above. Then check with your local building or health department to determine if they have other requirements.

On 2015-04-30 by Anonymous

need to know the size of septic tank required for a 3 brm home in the west kootenys

On 2014-11-24 by (mod) -

June,

If you buy or install a lightweight septic tank access opening cover, for safety it must be strong enough to not collapse when passed over by a person or a piece of equipment, and it mist be secure against being opened by a kid.mfalling into a septic tank is most often fatal. Beck with your septic tank suppliers for what they've got at hand. If you are up island you may need to import a cover from Campbell river or Nanaimo.

Beware of something home made that is unsafe.

On 2014-11-24 by Jue

We need a replacement septic man hole cover. Our old ones were made of concrete and are breaking apart. Looking for something light weight but able to walk on. And not trip over. Live on Vancouver island.

On 2013-03-26 by Jake

I'd like to know the size need for 30 people (up to 3000 gallons of water per day).

On 2013-02-14 by Anonymous

For 100 Users - Diameter of Cylindrical Septic tank is 1.8 m Internal diameter and 2.5 m length

On 2012-10-30 by deepak parkhi

i would like to know the size of septic tank for 100 users

On 2012-09-16 by (mod) - what is better Concrete or PVC septic tanks

Dave,

I think each tank material has pros and cons, and I'm doubtful that there is a single "right" answer.

A concrete tank is more likley to be built to tolerate being driven-over by the lawn tractor, but PVC tanks, by being lightweight, are easy to transport across a difficult-to-access site to where the tank is needed.

On 2012-09-13 by Dave

considering what is better Concrete or PVC tanks

On 2012-09-06 by dan fridenberg

in a two br home with two persons living in the home i am installing an aerobic sys. i no my tank is a 1000 gal but for the next two tanks what size should each one be and baby will make three.

On 2012-08-09 by Anonymous

John, your question is a good one because the answer is messy, or has several possible replies:

1. your local building department or health department will either allow continue using the existing tank or not - or in some cases will require a bigger septic tank and more drainfield capacity if more occupants or more bedrooms are being added - it's a local official decision.

You could reasonably argue that the total number of bedrooms at the property is NOT changing so neither should your septic system design requirements. Local decision, I can't speak for your guys.

2. In any event you should look at SEPTIC TANK PUMPING SCHEDULE (in the ARTICLE INDEX found at the end of this article) and pump your tank at a frequency based on size and number of occupants unless you have more sophisticated data like actual sludge and scum measurements, or if you use a "points system" method of determining septic tank pumping interval (also found in that article).

3, The septic tank size requirements that designers use are in the table in the article above and as you saw, are based on wastewater flow estimates - detailed

at SEPTIC SYSTEM DESIGN BASICS

and at WATER QUANTITY USAGE GUIDE

Found in the ARTICLE INDEX near end of this page.

On 2012-08-09 by John

I have a 3 bedroom 1 bath house. I am looking to knock out the wall separating a very small bedroom and a medium sized bedroom - turning 2 bedrooms into 1. Then I am looking to build a bedroom and a second bath in my unused garage.

The inspection report I have when I bought the house says I have a 1000+ gallon septic tank. Will this hold the additional bathroom or will the town make me replace the tank for a larger one?

On 2012-07-24 by (mod) - can I just add a bigger tank?

Gord, essentially, yes. But considering the costs involved, one would not rush to replace a 1000g septic tank with a 1200 gallon unit unless the original tank was damaged or otherwise needed replacement.

That added 200 gallons of capacity and thus improvement in settling out of solids and greases is expensively bought - most people would pump more often and defer the new septic tank.

On 2012-07-24 by gord

If you have to have a bigger tank installed is it as simple as just changing the size of the tank? i.e. 1000 gal - to 1200 gal.

On 2012-07-10 by (mod) - hazards of "outdated" septic tanks

Outdated septic tank: while I too am very pessimistic about the functionality of an old, under-sized, site-built concrete block septic tank (leaks into and out of the tank are likley as is tank collapse a risk), the symptoms you describe seem to mix up a drainfield failure with a septic tank failure.

If you had a 900 gallon capacity septic tank that were intact, that is not collapsed, and if it were pumped out - thus removing sludge and scum, you've got about 900 gallons of wastewater volume - the tank is filled in less than a week of normal use; septic tanks are normally "full" of wastewater all the time.

The overflowing waste into the yard is more likely to be a blocked effluent line or saturated drainfield - it sounds to me as if the entire SYSTEM needs replacement, is unsanitary, and thus in failure.

Your options: inform the owner that there is an unsafe (collapse risk) and unsanitary condition (backing up sewage onto the property surface) that make the building not only not habitable but at risk of issues with local code authorities.

I would be SURE to keep everyone away from the septic tank area; a collapsing masonry block septic tank, if someone falls in, is likely to be a fatality.

On 2012-07-10 by Outdated Septic Tank

I rent a home with an very outdated, cinder block constructed 900 gallon septic tank. The tank would need to be frequently drained (2-3 months) with just 2 people using a normal amount of water. The waste would overflow into the yard.

We were told by the company that pumped it u that it was not in compliance. What are our options as far as requesting it be replaced? We were told it isn't even a legitimate septic tank.

On 2012-06-09 by (mod) - can we add a bedroom and not enlarge the septic?

Karen, more frequent pumping can help protect the drainfield from damage, but nevertheless, if your system was designed fdor just 3 bedrooms, or nominally, 3-6 people, larger numbers of visitors risk overloading the drainfield with septic effluent - and shortening its life as well.

So in the short run the risk is contaminating the environment and in the longer run there is some risk that the high occasional usage, by overloading the system wastewater by volume, won't pemit enough settling time in the septic tank, thus pushing fine floating solids into the drainfled, clogging it.

On 2012-06-06 by Karen Rea

I have a similar question to one below - we have a purchase option on a summer house that clearly has 4 bedrooms, but the septic plan is only for 3 bedrooms - have no idea why (maybe because of the poor soil/ledge around it, as this is an island home in Maine?).

In fact, most of the time there will only be 2-4 people there, but we would like to rent it so there will be some periods of time with up to 8 people. There is only 1 bathroom with a shower, no dishwasher, but a washing machine. What are the implications for this - just more frequent pumping? Or should be convert one of the bedrooms to a study?

Thanks -

On 2012-05-23 18:21:28.577260 by pallavi

how to calculate septic tank size for an industrial building having factory with office and canteen and changing room?

On 2012-04-23 01:09:11.446345 by Sunil

Thanks Dan

On 2012-04-22 21:12:55.894611 by (mod) -

Sunil, its not my standard, i report on authorities' standards. My guess i they assume a max of 2 people per room

On 2012-04-22 21:10:54.671773 by (mod) -

Jenn, in my opinion you could be overliading the system, risking a failed leachfield even if you up the frequency of tank pumpout

On 2012-04-22 21:09:11.144833 by (mod) -

N.J. tank volume, to be accurate is based on interior measurements.

On 2012-04-22 16:00:44.025796 by Sunil

When you say 5-6 bedrooms how many people are you talking about?

On 2012-04-12 21:06:21.363379 by Jenn D.

We are in the process of buying a home with a septic system. The inspector passed the system for a 4 bedroom home; however, the house in question is a 6 bedroom duplex. We are planning on having 7 people reside in the home. Is this OK?

On 2012-04-03 02:51:12.486712 by N.J.

In calculating septic tank volume in gallons should the measurements come from inside wall to inside wall or outside wall to outside wall for length and width

On 2012-01-25 01:40:33.970353 by GORDON

Hi Professional, How could I calculate the total size of septic tank for a budget hotel with 138rooms??? What's the standard septic tank's size? How many do i need? How big areas do i need to allocate them?
Thanks alot.

On 2012-01-08 21:56:52.506529 by (mod) -

Kacy the question is unclear and leaves me guessing but I think you may be asking how far in horizontal distance a given volume of water discharted into a septic tank will cause effluent leaving the tank to travel in the drainfield.

I'm sure there is no simple "right" answer to that because the answer depends on quite a few local variables peculiar to the individual septic system installation, such as

- the number, diameter, placement, construction materials, and slope of the individual drainfield or soakaway bed leach lines

- the pre-existing saturation of or clogging of the soils around the leach lines

- the age of the septic system and conditions of the drainfield soils

- the amount of time since the last effluent dose

- the season of year and soil water levels

For example, four wide-diameter chamber type or wide gravel ditch drainfield trenches in good working order and receiving a uniformly-distributed dose of effluent from the septic tank and D-box will absorb the volume of water entering the trench quickly, near the entry point while a single line drainfield trench of small diameter, of much longer length, in old condition with clogging of soils already present in the front end of the line, will send an equivalent septic effluent volume much further along in the line than the first case.

On 2012-01-07 06:32:12.115687 by kacy

How can I calculate the total distance covered by a wastewater that is discharged into a baffled septic tank at once.

On 2011-08-08 16:25:11.734042 by (mod) -

Thank you so much, Angela and Helsy.

InspectAPedia is an independent publisher of building, environmental, and forensic inspection, diagnosis, and repair information for the public - we have no business nor financial connection with any manufacturer or service provider discussed at our website.

We are dedicated to making our information as accurate, complete, useful, and unbiased as possible: we very much welcome critique, questions, or content suggestions for our web articles. Working together and exchanging information makes us better informed than any individual can be working alone.

On 2011-08-07 22:21:57.182347 by Angela

The info was very helpful & easy to understand. Thanks for doing what you do!

On 2011-08-07 07:45:44.862111 by helsy

thanks!

On 2011-08-06 23:54:15.719537 by (mod) -

The excavation dug to accept the septic tank is just enough larger than the physical dimensions of the tank to allow the tank to be lowered into the opening, plus space to make the connections to the incoming and exiting waste piping. The depth is determined also by the depth of inlet and outlet waste piping and the drainfield if the tank is to drain by gravity, or by the elevation of the pumping chamber if the tank is to be drained by a pump.

On 2011-08-06 23:17:42.329204 by ursula

How big does a septic pit need to be for a 1000gl tank ?

On 2011-06-13 10:51:56.538263 by timothy

very simple and easy to understand. thanks

...

Continue reading at SEPTIC TANK SIZE - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see SEPTIC TANK SIZE FAQs-2 - more-recent questions and answers posted on specifying the right size or capacity for a septic tank.

Or see these

Recommended Articles

• SEPTIC DRAINFIELD SIZE
• SEPTIC DRAINFIELD LOCATION for help in finding an existing septic soakaway bed, leach field or drainfiield
• SEPTIC TANK, HOW TO FIND
• SEPTIC TANKS, CONCRETE
• SEPTIC TANKS, FIBERGLASS / PLASTIC
• SEPTIC TANKS HOME MADE SITE BUILT
• SEPTIC TANK LEVELS of SEWAGE
• SEPTIC TANK PUMPING SCHEDULE
• SEPTIC TANK SIZE - topic home
• SEPTIC TANK SIZE vs SEWAGE FLOW
• SEPTIC TANKS, STEEL

Suggested citation for this web page

SEPTIC TANK SIZE FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to SEPTIC SYSTEMS

Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia

Ask a Question or Search InspectApedia

Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Note: appearance of your Comment below may be delayed: if your comment contains an image, photograph, web link, or text that looks to the software as if it might be a web link, your posting will appear after it has been approved by a moderator. Apologies for the delay.

Only one image can be added per comment but you can post as many comments, and therefore images, as you like.
You will not receive a notification when a response to your question has been posted.
Please bookmark this page to make it easy for you to check back for our response.
Our Comment Box is provided by Countable Web Productions countable.ca

Citations & References

In addition to any citations in the article above, a full list is available on request.

---

ADVERTISEMENT

---