Roof Pitch Calculator
Enter rise and run to get your roof pitch as X:12, the angle in degrees, percentage grade, and the slope multiplier used to estimate roofing material.
Pitch
6:12
Angle
26.6°
Slope
50%
Slope factor
1.118×
Slope factor is the multiplier for converting flat (footprint) area into actual roof surface area — multiply your footprint square footage by this number when ordering shingles or underlayment.
How the roof pitch calculator works
Roof pitch describes how steep a roof is, expressed as the inches of vertical rise for every 12 inches of horizontal run. This calculator takes your rise and run and converts them into the four numbers roofers and suppliers actually use:
- Pitch (X:12) — the standard notation used on blueprints and material spec sheets.
- Angle in degrees — useful for setting a miter saw or speed square.
- Percentage slope — used in some engineering and drainage calculations.
- Slope factor— the multiplier that converts your home's flat footprint area into true roof surface area for ordering materials.
Formula: pitch = (rise ÷ run) × 12. Angle = arctan(rise ÷ run). Slope factor = √(rise² + run²) ÷ run.
Frequently asked questions
It means the roof rises 6 inches vertically for every 12 inches (1 foot) it runs horizontally. The first number is always the rise; the second is conventionally 12.
Hold a 12-inch level flush against the roof surface, then measure straight down from the 12-inch mark to the roof with a tape measure — that measurement is your rise. If you already know the roof height and building width, rise = height and run = half the building width.
Under 4:12 is generally considered low-slope and often needs different roofing materials (like membrane roofing). 4:12 to 9:12 is a standard pitch most shingles are rated for. Above 9:12 is considered steep and usually requires extra fall-protection and labor.
Roofing material is sold by actual surface area, not the flat footprint of your house. Multiply your building's footprint square footage by the slope factor to get the true roof area, then add 10-15% waste for cuts and overlaps.