Roof Pitch Calculator
The roof pitch calculator finds the length of the rafter and the roof slope (in degrees and in percent).
Pitch6 in 1226.565° from horizontal
Angle26.5651°
Pitch multiplier1.118034multiply a horizontal length or area by this to get the sloped one
Grade50%
As a fraction of span0.25the older British way of quoting a pitch
Rise per foot of run6 in
Walkable?yesup to about 6 in 12 most people can work on it
Suits shingles?yesasphalt shingles want 4 in 12, and 2 in 12 is the absolute floor
Ridge height above the plate7.5 ft7 ft 6 in
Common rafter length16.771 ft16 ft 9.25 in, plate to ridge, no overhang
Roof area per foot of building length33.541 sq ft30 ft span × 1.11803, both slopes
The method
pitch = rise ÷ 12 run; multiplier = √(rise² + run²) ÷ run
The multiplier does all the work
Roof pitch is quoted as inches of rise per 12 inches of run. The useful number that follows is √(rise² + run²) ÷ run: multiply any horizontal distance or area by it and you get the sloped one. For a 6 in 12 roof that is 1.1180, so a 1,000 square foot footprint has 1,118 square feet of roof.
Pitch also decides what can go on the roof. Asphalt shingles need at least 4 in 12 to shed water reliably, and between 2 and 4 in 12 they need a doubled underlayment. Below 2 in 12 shingles will leak whatever you do — that is membrane territory.