Roof Pitch Angle Calculator

Roof pitch from rise and run or an angle: degrees, x:12 pitch and slope percent, with a slope class. A 6-in rise over a 12-in run is 26.57°. How it works

Rise

Run

Roof angle

26.57°

Pitch 6:12 · Slope 50%

Slope Class

Medium Slope

Above the 2:12 to 4:12 band where asphalt shingles need double underlayment.

Quick Reference

1:12

4.76°

2:12

9.46°

4:12

18.43°

6:12

26.57°

8:12

33.69°

10:12

39.81°

12:12

45°

14:12

49.4°

About the Roof Pitch Angle Calculator

A roof that rises 6 in over 12 in of run is a 6:12 pitch, 26.57° or a 50% slope. Pitch is rise ÷ run × 12, the angle is atan(rise ÷ run) and the percent is rise ÷ run × 100. This roof pitch calculator works from a rise and a run in the same unit, or from an angle and a run (rise = run × tan(angle)), and the table on this page gives degrees for the common x:12 pitches.

Common roof pitches in degrees and percent

Pitch	Angle	Slope	Tool’s slope class
1:12	4.76°	8.33%	Low Slope
2:12	9.46°	16.67%	Low Slope
3:12	14.04°	25%	Low Slope
4:12	18.43°	33.33%	Medium Slope
5:12	22.62°	41.67%	Medium Slope
6:12	26.57°	50%	Medium Slope
7:12	30.26°	58.33%	Medium Slope
8:12	33.69°	66.67%	Steep Slope
9:12	36.87°	75%	Steep Slope
10:12	39.81°	83.33%	Steep Slope
11:12	42.51°	91.67%	Steep Slope
12:12	45°	100%	Very Steep

Each row is a rise of the pitch number over a run of 12. The slope classes are this tool’s own bands, not terms from a building code.

How to use this tool

Measure the rise (vertical height) and the run (horizontal distance) over the same stretch of roof.
Type both numbers. The fields say inches, but any equal units give the same pitch. If you have an angle instead, switch to Angle and type the degrees and a run.
Read the angle, the x:12 pitch, the slope percent and the slope class.

Frequently asked questions

How do I convert roof pitch to degrees?: Divide the pitch number by 12 and take the arctangent. For 6:12, atan(6 ÷ 12) = 26.57°. For 4:12 it is 18.43° and for 12:12 it is 45°.
What is a 4/12 roof pitch in degrees and percent?: 18.43° and a 33.33% slope. It is the first row the tool calls Medium Slope.
What pitch is a 45 degree roof?: 12:12, a rise of 12 in for every 12 in of run, which is a 100% slope. For any angle, rise = run × tan(angle): in Angle mode, 30° over a 12 in run gives a 6.93 in rise, 6.93:12 and 57.74%, and 26.565° gives 6:12.
What is the minimum roof pitch for asphalt shingles?: A building department page on section R905.2 says asphalt shingles may only be used at 2:12 (9.46°) or steeper, and that slopes from 2:12 to 4:12 need double underlayment. The tool’s notes repeat those limits. Local codes and manufacturer instructions can differ, so confirm with your building department.
How do I measure roof pitch?: Hold a level horizontal against the roof, measure 12 in along it, then measure straight up or down from that mark to the roof surface. That vertical distance is the rise in x:12. Any other rise and run pair works too: 10 in over 24 in is 5:12.
What counts as a flat roof?: Here, any pitch below 1:12 is shown as Flat. That cutoff is this tool’s own, not a building code definition, so a roof the tool calls Flat may still have a small slope. A rise of 0 gives 0°, 0:12 and 0%.

Reading a roof's slope

Plans and roofers give slope as a pitch such as 6:12, apps and inclinometers give degrees, and some product sheets give a percent. All three come from the same rise and run: a 6:12 roof is 26.57° and 50%, a 3:12 roof is 14.04° and 25%. The fields are labeled in inches, but any unit gives the same pitch as long as rise and run use the same one, and the 1,200 limit then applies in that unit.

If an app gave you degrees, switch to Angle and type the angle and a run: 30° over a 12 in run is a 6.93 in rise, 6.93:12 and 57.74%. A drawing under the result shows the run, the rise and the angle to scale.

The angle is the roof's slope from horizontal. It is not a saw setting, since the cut angle on a rafter depends on which cut you make. The slope class note under the result flags the asphalt shingle limits: nothing below 2:12, and double underlayment from 2:12 to 4:12.

Pitch, angle and percent

angle = atan(rise ÷ run)

pitch = rise ÷ run × 12, written pitch:12

slope % = rise ÷ run × 100

rise = run × tan(angle) in Angle mode, for an angle above 0 and at most 89.9°

A 6:12 roof rises 6 in for every 12 in of run: atan(6 ÷ 12) = 26.57°, a slope of 50%. A 12:12 roof is 45° and 100%. A rise of 0 is a flat roof at 0°. Rise may be 0 to 1,200 and the run must be above 0 and at most 1,200. Results are rounded to two decimals. The slope class is this tool's own band, not a code term: under 1:12 Flat, 1:12 up to 4:12 Low Slope, 4:12 up to 8:12 Medium Slope, 8:12 up to 12:12 Steep Slope, and 12:12 and over Very Steep. The note beside each class names the shingle limit where it applies. Measure the run horizontally, not along the rafter.

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