Roof Pitch Calculator · Free calculator

6/12 Roof Pitch Calculator

A 6/12 roof rises 6" for every 12" of run — an angle of 26.57° and a rafter multiplier of 1.118. It's a conventional (walkable up to ~6/12) roof. Rise and rafter lengths for common runs are below.

Quick answer

Angle: 26.57°
Slope factor: 1.118
Grade: 50.0%
Rafter per ft of run: 1' 1-7/16"

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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

6/12 rise and rafter length by run

Run = half the building span. Rafter length is ridge to building line, no overhang.

Run	Total rise	Rafter length
4'	2' 0"	4' 5-11/16"
6'	3' 0"	6' 8-1/2"
8'	4' 0"	8' 11-5/16"
10'	5' 0"	11' 2-3/16"
12'	6' 0"	13' 5"
14'	7' 0"	15' 7-13/16"
16'	8' 0"	17' 10-11/16"

Roof pitch comparison 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

Angle = arctan(rise ÷ run) = arctan(6 ÷ 12) = 26.57°
Slope factor = √(12² + 6²) ÷ 12 = √180 ÷ 12 = 1.1180
Grade = 6 ÷ 12 × 100 = 50.0%
Rafter length = run × 1.1180

Trade pro tips

Asphalt shingles are fine at this pitch with standard underlayment.
Up to about 6/12 most roofers can walk the roof without jacks.
Measure pitch in the attic: level 12" off a rafter and measure straight up to its bottom edge.

Frequently asked questions

What angle is a 6/12 roof pitch?

26.57 degrees (arctan 6/12). The plumb cut on a rafter is 26.6° and the seat cut is 63.4°.

What is the rafter multiplier for a 6/12 pitch?

1.1180. Multiply the run (in feet or inches) by it to get the rafter length: a 12 ft run gives 13' 5".

Is a 6/12 roof steep?

A 6/12 roof (26.6°) is conventional (walkable up to ~6/12).

What is 6/12 pitch as a percentage?

50.00% grade — the roof rises 6 inches per foot, or 0.500 ft per ft.