# The pitch of a roof



## English Roofer (Dec 26, 2008)

Hi guys, i have a question, you guys ,when you talk of pitch of a roof say the pitch was less than 4:12 etc, im not sure what that actually means we say in degrees as in a 33 degree roof, can some one explain please?
Cheers
Dave


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## Mike Lamb (Nov 12, 2008)

http://roofgenius.com/roof-pitch-degrees.asp

It's the inch rise of the roof every horizontal 12" or one foot run. It's probably a US thing. For instance, I didn't know 50 mm is about 2". I had to go to a metric conversion chart. A 4:12 = 18.5 degrees.


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## Grumpy (Oct 29, 2008)

4:12 means that for ever 12" horizontally I travel, I am moving 4" vertically. If you take a right-triangle and the base is 12", the side will be 4". the sidSame thing Mike said above, but I felt like typing it too


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## English Roofer (Dec 26, 2008)

Cheers Guys that explains it!


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## Ed the Roofer (Sep 15, 2008)

It would still translate the same way in metric versus US standard, by the way.

Ed


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## GreenTree (Mar 13, 2009)

And you convert slope (4:12) to degrees using tan. So, tan(x) = 4 / 12 where x is the slope in degrees. 
tan(x) = 0.3333
x = atan(0.3333)
x = 18.4 degrees


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## English Roofer (Dec 26, 2008)

GreenTree said:


> And you convert slope (4:12) to degrees using tan. So, tan(x) = 4 / 12 where x is the slope in degrees.
> tan(x) = 0.3333
> x = atan(0.3333)
> x = 18.4 degrees


Thanks for that!:thumbup:


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## Jared (Jul 9, 2012)

My math is apparently off by a little. A 12/12 is 12 units rise per 12 units run, .I figure that to be a 45 degree angle. By that logic i calculate a 4/12 (1/3 of 12/12) to be 15 degrees. 

Where am I going wrong?


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## Jared (Jul 9, 2012)

Nevermind, its trig and I never took it in school. Guess I'm stuck wondering how it works. Makes me feel pretty stupid.


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## Jared (Jul 9, 2012)

I know that its not a linear function, its determined by the arctan. Whatever the hell that is.


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## karankundra (Nov 28, 2011)

The pitch of a roof is determined by the angle of descentfrom the most important thing about the pitch of a roof is its slant. The higher the angle is the more protected it will be. A pitch is measured by the run and rise. For example, a 4/12 pitch means the roof rises four inches for every twelve inches it runs



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