Roof Pitch Calculator · Free calculator

Roof Pitch Calculator

Enter the rise and run you measured (or pick a common pitch) to get the angle, slope factor and grade. The full chart below covers 1/12 through 12/12.

Quick answer

4/12: 18.4°
6/12: 26.6°
8/12: 33.7°
12/12: 45°

▍Roof Pitch Calculator

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Roof pitch

6/12

26.6° · 50.0% grade

Angle

26.57°

Slope factor

1.118

Grade

50.0%

Rafter / ft run

13.42in

Roof pitch chart

Pitch	Angle	Slope factor	Grade	Class
1/12	4.76°	1.003	8.3%	flat / low-slope
2/12	9.46°	1.014	16.7%	low-slope
3/12	14.04°	1.031	25.0%	low-slope
4/12	18.43°	1.054	33.3%	conventional
5/12	22.62°	1.083	41.7%	conventional
6/12	26.57°	1.118	50.0%	conventional
7/12	30.26°	1.158	58.3%	conventional
8/12	33.69°	1.202	66.7%	conventional
9/12	36.87°	1.250	75.0%	steep
10/12	39.81°	1.302	83.3%	steep
11/12	42.51°	1.357	91.7%	steep
12/12	45.00°	1.414	100.0%	steep

How the math works

Pitch = rise per 12" of run.
Angle = arctan(rise ÷ 12).
Slope factor = √(12² + rise²) ÷ 12.
Rafter length = run × slope factor.

Trade pro tips

Measure pitch with a level and tape: hold the level 12" level from the roof surface and measure the vertical gap.
Pitch apps on phones are close, but a 2-ft level is more reliable on rough shingles.

Frequently asked questions

How do I calculate roof pitch?

Measure the rise over a 12" level run. A 6" rise over 12" is a 6/12 pitch. Or divide total rise by run and multiply by 12.

What is the most common roof pitch?

Between 4/12 and 9/12; 6/12 (26.57°) is the most common on US homes.

What is the minimum pitch for shingles?

2/12 with double underlayment; 4/12 and up with standard underlayment (IRC R905.2.2).

How do I convert roof pitch to degrees?

Degrees = arctan(rise ÷ 12). 4/12 = 18.43°, 6/12 = 26.57°, 8/12 = 33.69°, 12/12 = 45°.