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15/12 roof pitch in degrees

A 15-in-12 roof — 15 inches of rise for every 12 inches of run — as an angle, a percent grade, a slope ratio, and the rafter length it adds per foot of run.

15/12 pitch =

=51.34°

Angle

51.34°

Percent grade

125%

Slope ratio

1.25

Rafter / ft of run

1' 7-3/16"

What it means on the roof

Set a speed square to 51.34° for the plumb and seat cuts. Every foot of horizontal run adds 1' 7-3/16" of common-rafter length, so a run of 10 ft makes a rafter about ten times that. The percent grade (125%) is the same slope a road sign or a laser level reads.

Nearby pitches

Pitches around 15/12

Pitch	Angle	Grade	Rafter / ft run
12/12	45.00°	100%	1' 5"
13/12	47.29°	108.3333%	1' 5-11/16"
14/12	49.40°	116.6667%	1' 6-7/16"
15/12	51.34°	125%	1' 7-3/16"
16/12	53.13°	133.3333%	1' 8"
17/12	54.78°	141.6667%	1' 8-13/16"
18/12	56.31°	150%	1' 9-5/8"

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