Roof Area & Pitch Calculator — ft, rise:run, degrees

How to Calculate Roof Area from Pitch

Measured plan dimensions only give the footprint a roof covers — the real sloped surface is always larger. This tool multiplies the footprint by the pitch factor √(1+(rise/12)²) so material take-offs match what actually gets installed. Enter the footprint plus pitch, raw rise and run, or a degree angle; choose gable, hip, or shed; and read off actual area, roofing squares, rafter length, ridge and hip lengths. Add extra sections for dormers and L-shaped wings.

How to use

Pick an input mode. Footprint + pitch is fastest for new work where you know the building outline and a specified pitch. Rise + run suits field-measured existing roofs. Degrees is for plans dimensioned by angle. Order shingles or panels from the actual area, not the footprint — feed the result into the shingles bundles & cost calculator or the metal roofing panels calculator. Low-slope sections under 2:12 are not shingle territory — size those with the flat roof membrane calculator instead.

Formulas

Pitch factor (PF) = √(1 + (rise/12)²). Angle = arctan(rise/12) in degrees. Rafter run length = horizontal run × PF. Gable / shed area = footprint area × PF. Hip area = footprint area × PF (all four planes share the same pitch, so footprint × PF still holds). Roofing squares = actual area ÷ 100. Add 10% waste for simple gables, 15% for hip and cut-up roofs before ordering.

Common pitches

2:12 = 9.5° (minimum slope for asphalt shingles, PF 1.014) · 4:12 = 18.4° (standard residential, PF 1.054) · 6:12 = 26.6° (PF 1.118) · 8:12 = 33.7° (PF 1.202) · 12:12 = 45° (PF 1.414, equal rise and run).

FAQ

What is a roofing square? One square = 100 ft² of roof surface. Shingles, underlayment, and most roofing are quantified by the square; architectural shingles run about 3 bundles per square plus separate starter and ridge cap.
Does the pitch factor change for hip roofs? No. Every plane of a uniform-pitch hip carries the same PF, so actual area is still footprint × PF — the hip just redistributes rafters into hip and jack rafters. Get rafter stock lengths from the board feet lumber calculator and downstream drainage from the gutter & downspout calculator.
Why is rafter length longer than the run? The rafter follows the slope, so its length is the horizontal run times the pitch factor — always longer than the run itself.

On install day

Three things estimators forget on a tear-off. Drip edge — IRC R905.2.8.5 requires it at every eave and rake; 10 ft pieces with 2″ overlap, so order LF ÷ 9.8 (not ÷ 10). Starter and ridge cap are separate from field shingles — one bundle of starter covers ~120 lf of eave, one bundle of hip-and-ridge covers ~30 lf. Asphalt shingles run roughly $4–6/ft² installed for 3-tab and $5–8/ft² for architectural in 2025 USA pricing; metal panels $8–14/ft²; standing seam $12–20/ft². Waste — bump to 15% on any hip or cut-up roof and 20% with dormers; valleys, ridges, and starter cuts eat material faster than the napkin math suggests. For ordering, feed the area-plus-waste value into the shingles bundles calculator.