Roof slope, pitch, rise, run, area calculation questions & answers.

Q&A on how to convert roof angle to rise and other roof slope, rise, run calculation methods.

This article series gives clear examples just about every possible way to figure out any or all roof dimensions and measurements expressing the roof area, width, length, slope, rise, run, and unit rise in inches per foot.

Q&A on How to Calculate or Convert the Roof Slope, Angle, Degree, Grade, Percent, Height, Rise, Run

These questions & answers on roof angle, slope, rise, run conversion or calculation were posted originally

at ROOF SLOPE CALCULATIONS - be sure to review that article.

On 2018-10-06 by bp - what is the rise of a 3 degree sloped roof?

What is the RISE at 3 Degree pitch at 2200 mm & 4800 mm ?

On 2018-10-06 by (mod)

Did you try the procedure given at the start of the article ROOF SLOPE CALCULATIONS ?

Let's recap how we convert roof slope in degrees to a horizontal rise:

How to Calculate the Roof Slope (or any slope) Expressed as Rise & Run from Slope Measured in Degrees

It's easier than it looks. But you'll need a calculator.

I can tell you that 3 degrees gives you a rise of less than 1 inch in 12 inches of run.

More help:

Using any geometry book or online TANGENTS TABLE of tangent values we will find the tangent of 3 degrees

What's a "tangent" - it's a fraction, expressed as a decimal value, that we can get for the ratio of two sides of right triangle: the tangent of angle X is

Opposite Side Length / Adjacent Side Length for the angle X

(At the companion article we cited at the start of this page we also show how to calculate tangents but we'll skip that for now)

For your 3 degree slope case:

tangent (3°) = 0.05241

Therefore for your roof,

0.05241 = Rise / Run

If I assume the two numbers you gave, 2200 mm and 4800 mm, are horizontal distance or "run", then we can solve the equation by simple algebra, writing

0.05241 = Rise / Run where run = 2200

0.05241 = Rise / 2200

2200 x 0.05241 = Rise

115.302 = Rise

Or a roof rise of about 115 mm.

and
0.05241 = Rise / Run where run = 4800

0.05241 = Rise / 4800

4800 x 0.05241 = Rise

251.568 = rise - or about 252 mm

 

In the remaining Q&A below the original question will be found below the moderator's reply.

On 2018-10-05 by (mod) - What is the pitch of a 7 foot ridge pole 20 foot wide building

Glad to help anon.

A 7 foot high ridge pole, assuming we are taking the height from the top surface of the pole, means that the roof rises seven feet above the attic floor.

A 20 foot wide building, assuming that's the width between the outer surface of the walls, means that the length of the bottom of a roof triangle describing the roof slope will be half that, or ten feet.

So we have a roof that rises up 7 feet over 10 feet of horizontal run.

Or in inches, (7x12) / (10x 12) (since there are 12 inches in a foot.

that's 84" / 120"

Now to get the pitch or slope of the roof expressed the conventional way of inches of rise per foot of run, we could just to divide both the numerator and denominator of the roof fraction by 10.

(Since we observe that the denominator or 120 inches will convert neatly to one foot by dividing by 10)

84/10 = 8.4
and

120/10 = 12

So we have 8.4" of rise in 12" (or one foot) of run.

It's an 8.4/12 roof. or an 8.4 in 12 roof.

----

We could have also done the calculation like this.

A roof that rises 7' in 10' of run has a rise of 7 tenths of a foot of rise in 1 foot of run or 7/10 of a foot slope.

7/10 can be written as 0.7 (that's 7 tenths in decimal).

To convert that to inches of rise per foot of run we would multiply

0.7 x 12 (inches in a foot) to get 8.4 inches of rise per foot of run
or again

an 8.4/12 slope roof.

On 2018-10-05 by Anonymous

What is the pitch of a 7 foot ridge pole 20 foot wide building

On 2017-04-06 by Anonymous

Malayalathil parayamo

On 2017-02-14 by (mod) -

Not unless you use an appropriate waterproof underlayment

On 2017-02-13 by ken

my extension is 13ft long the hight 9ft at one end 8ft at the other will there be enough pitch for tiles

On 2016-12-28 by (mod) -

The horizontal run doesn't of course give the rise. That's a design decision. I'd consider climate, architecture, roofing material. Generally a steeper roof sheds water better and lasts longer.

On 2016-12-28 by BALIRE

My concern is that, how do I determine the suitable roof rise for a building in case I do not yet have the roof slope but have only the span or the run?
Thank you for your kind co-operation.

On 2016-10-17 by Anonymous

23 degree of 7 feet on a roof

On 2016-10-08 by Ishmael Lawes.

I just asked a question and realised Google is educational to people who want to learn.

On 2016-09-12 by (mod) - falsely accused of cheating, skipped learning geometry

Thanks so much Ramon. I too had to struggle through the formulas to understand them. Figuring out how to explain something is a great way to learn it ones self.

In 5th Grade I was taking a math test. On the cover of the test, folded double, we were to sign a pledge that we had neither given nor received help on the test. I turned in my paper but forgot to sign the pledge.

So I went back to the teacher's desk (she was out of the room) to sign my name.

Mrs. Revere (we called her Mrs. Severe) came in and saw me writing on a paper at her desk and assumed I was cheating. (I never cheated, I'd rather fail.). Mrs. Severe ripped up my paper and sent me out for cheating.

That bad day was enough to steer me away from math for a long time. In my school we could study Spanish instead of Math so I took Spanish and moved to Mexico.

Years later in programming school and in response to "I never took math past 5th grade) a kindly advisor (at IBM SRI) told me that I actually could do the math. It was a fun discovery.

On 2016-09-12 21:27:55.406116 by Ramon H.C. Addison. Onebarney@yahoo.com

I haven't done any critical problems in math for years. This info has been extremely beneficial to me, not to mention exciting and interesting. Didn't think I would ever embrace math again.

...

Continue reading at ROOF SLOPE CALCULATIONS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• ARCTANGENT CALCULATES ROOF / STAIR ANGLE
• CALCULATE RISE & RUN from SLOPE
• ROOF SLOPE CALCULATIONS
• ARCTANGENT CALCULATES ROOF / STAIR ANGLE
• CONVERT PERCENT GRADE to ANGLE or SLOPE
• CONVERT ROOF SLOPE or ANGLE in DEGREES to RISE or RUN
• CALCULATE ROOF HEIGHT from SLOPE & RUN or BUILDING WIDTH
• CALCULATE RAFTER LENGTH from SLOPE & RISE
• CALCULATE the TAN VALUE from TWO SIDES of a TRIANGLE
• CALCULATE ROOF TRUSS LENGTH FROM ROOF RISE
• DEFINE & USE TANGENTS for BUILDING ROOFS, STAIRS
• ROOF SLOPE TABLE, TYPES, WALKABILITY
• ROOF MEASUREMENTS - all of the methods for measuring roof slope, area, etc.
• TANGENT & SLOPE CALCULATIONS

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ROOF SLOPE CONVERSION FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING ROOFING

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