Roof Pitch Calculator
Calculate roof pitch from rise and run such as 6 in 12, plus slope angle and percent grade. Use it to match shingles, framing, and drawings.
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What the roof pitch calculator does
Roof steepness gets described in a few different ways, and the one you need depends on who you are talking to. A roofer wants it as 6 in 12, a framer might want the angle in degrees, and a drainage drawing might call for a percent. This converts between them all. You enter the roof either as a rise and run, or as an angle, and it gives you the pitch, the angle, the grade, and the slope.
It is the translator between the way a roof is drawn, framed, and covered. Below is how the numbers relate and what each one is for.
How to use it
- Choose how you are entering the roof. Rise and Run if you have measured it, or Angle in Degrees if you already know that.
- For rise and run, enter both with their units. You can mix units, since the calculator works with the ratio between them.
- For an angle, enter a value between 0 and 90 degrees.
- Press Calculate for the conversions, or Reset to clear it.
How pitch, angle, and grade relate
They are all just different ways of stating the same triangle of rise over run. Roof pitch in the US is written as the rise for every 12 inches of run, so a roof that climbs 6 inches across 12 inches of level distance is a 6 in 12, written 6:12:
Pitch = (rise ÷ run) × 12, written as that number in 12
The angle is the same slope read as degrees, using the arctangent of rise over run. The grade is that slope written as a percent, which is just rise over run times 100. So a 6:12 roof rises at 26.6 degrees and has a 50 percent grade, three names for one steepness.
Reading the four numbers
The result gives you four ways to describe the slope, and each has its place. The pitch, the X:12 figure, is what roofers and shingle wrappers use. The per foot figure is the rise across a foot of run, handy at the saw. The grade, the percent, turns up on site plans and drainage drawings. And the angle in degrees is what you dial into a saw or a digital level.
One thing worth keeping straight: a percent and an angle are not the same number. A 100 percent grade is a 45 degree angle, not 100 degrees, because percent is rise over run while degrees measure the actual angle.
A worked example: a 6 in 12 roof
Say you measure a rise of 6 inches over a run of 12 inches.
The pitch is 6 in 12, since the run is already 12. The grade is (6 ÷ 12) × 100 = 50 percent. The angle is the arctangent of 6 over 12, which is about 26.6 degrees. And the rise per foot is, of course, 6 inches.
So the same roof is a 6:12, a 50 percent grade, and a 26.6 degree slope, depending on which drawing or trade you are speaking to.
Why pitch matters for your roof
Pitch is not just a label; it decides what can go on the roof. Standard asphalt shingles need a slope to shed water, so most manufacturers want at least a 4 in 12, with special low-slope methods allowed down to about 2 in 12. Below that, shingles are not rated and you move to a membrane roof. Metal panels handle lower slopes than shingles, which is part of why they suit shallow roofs.
Steeper roofs shed water and snow faster and give more attic space, but they use more material for the same footprint and are harder to work on. So the pitch ties together the look, the materials, and how the roof is built.
Questions people ask
What does a 6/12 roof pitch mean?
The roof rises 6 inches for every 12 inches of horizontal run. That works out to a 50 percent grade and about a 26.6 degree angle.
How do I convert roof pitch to degrees?
Take the arctangent of the rise divided by the run. For a 6:12 that is arctan(6 ÷ 12), which is about 26.6 degrees. The calculator does it for you.
What is a good roof pitch?
Most homes sit between 4:12 and 9:12. Around 4:12 to 6:12 balances looks, drainage, and cost, while steeper roofs shed snow better but cost more to build and cover.
Is pitch the same as slope?
In modern US usage, pitch, slope, and angle are used to mean the same steepness. The calculator shows it as a ratio, a percent, and an angle so any of them is to hand.
References
A quick note on the numbers. The conversions between pitch, angle, and grade are pure trigonometry, the arctangent of rise over run and its percent and ratio forms. The minimum slopes for each roofing material come from the roof-covering provisions of the International Residential Code. The unit conversions follow the US National Institute of Standards and Technology guide.
- International Code Council, International Residential Code, Chapter R905 (minimum slopes for roof coverings). https://codes.iccsafe.org
- National Institute of Standards and Technology (NIST), Special Publication 811, Guide for the Use of the International System of Units (SI). https://www.nist.gov/pml/special-publication-811
Mahendra Thapaliya is a graduate student in Structural Engineering at the University of Bologna, with research interests in structural systems, FEM, earthquake engineering, and numerical modeling. At Eon Tools, he reviews construction tools.