The Roof Pitch Calculator tools below will help you calculate the slope from every possible angle. Each tool performs a specific operation that involves measuring and calculating the slope.
Using this Pitch Calculator(s), you can calculate slope, area, rafter length and other dimensions, and convert Pitch to Degrees (at the bottom). We will explain how to measure roof pitch, using simple tools.
1) Calculate Slope based on Rafters Length:
Roof Span:  ft.  in. 
Roof Rise:  ft.  in. 
Roof Pitch = / 12″ 
How to use Roof Pitch Calculator:
To estimate roof area, enter width and length (as shown in the measuring diagram below), and either Rise or Pitch – second value will autocalculate. Click calculate. The results will pop below the calculate button, and will include: Rafter Length, Total Size / Area, and Pitch.
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Using the diagram below, measure your roof from the ground, and enter building dimensions into the calculator #2 above. Enter the span (also known as gable side width), and the rise above the base line.
To calculate your pitch and size, measure your roof and plug in your measurements in accordance with the diagram below. Enter EITHER Roof Rise or Roof Pitch.
2) Pitch to Angle (Degrees) Calculator – enter pitch in the first box – calculation is automatic.
Enter Roof Pitch:  / 12″ 
Results:  degrees angle 
Measuring roof rise:
If you do not know the rise, and do not have a ladder or cannot access your roof in order to measure it, you can accurately estimate the rise by measuring 3 spans of siding (typical vinyl siding has 4″ exposure, so 3 spans would be equal to 12″ or 1 foot), and calculating the number of spans from the base line to the peak. Since most homes have a Rake wood, which is usually 68″ wide, you can add that width to the rise.
Example: If you have 19 spans of siding at 4″ exposure (width) of each span, and a 6″ rake board, the rise would be:
[6″ + (19 * 4″)] / 3 = 6′ 10″ roof rise.
Converting pitch (US / Canadian slope measuring method) to degrees (European slope measuring method) can be useful in figuring out the roof geometry, or for roofers from Europe who are not accustomed to US system. See Table below:
Related article:
Asphalt Shingles Calculator – estimate cost of materials, using our tool here.
Average Roof Replacement Cost:
Low End
$4990

Mid Range
$6238

High End
$7798

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if 12/12 is 45°, why is not 6/12 = 22.5°?
also tool above says my pitch is “NaN/12″
Pa,
Quick answer – because it is not a straight line increase of 3.75 degrees, for each 1/12″. I will look into why you are getting “NaN”
from what i know of angles and degrees 12/12 is 45 degrees, so 1/2 of that is 6/12 or 22.5 degrees.
PA,
If we use that logic, then 24 pitch roof should be 90 degrees, right (12*2 same as 45 degrees * 2)? But it’s not. It’s about 63.5 degrees. Like I said – it is not a straight line. Each step is smaller than the previous one. Look at last diagram:
1 pitch is 4 degrees.
2 pitch is 9.5 degrees – that’s a 5.5 degrees step.
3 pitch is is 14 degrees – that is a 4.5 degrees step.
from there it slowly declines or stays the same…
However, those are not exact numbers – it’s more like 14.04 degrees for a 3 pitch.
These roof pitches are treated as right triangle, and by applying the theory, the inverse tangent of 6/12 is actually 26.565 degree.
This is very helpful, thank you.