Roof Pitch Calculator
Free roof pitch calculator. Convert roof rise and run into pitch (x/12), angle degrees, grade %, and slope factor for area estimates.
What is a roof pitch calculator?
A roof pitch calculator converts the rise and run of a roof into pitch (inches per 12 inches of run), the angle in degrees, grade percentage, and the slope factor used to convert floor area to actual roof area.
How this calculator works
- Enter the rise (vertical) and run (horizontal) in inches.
- Pitch = rise ÷ run × 12, giving the standard “x-in-12” format.
- The angle is the arctangent of the slope; the slope factor is the hypotenuse ratio.
- All four figures update together so you can use whichever your plans quote.
How to use the result
- Multiply your home’s footprint area by the slope factor to get the actual roof surface — that’s the number contractors price.
- Compare pitches: a 6/12 roof is ~27°, a 12/12 is 45°, and anything over 9/12 is steep and costs more to work on.
- Use the angle for solar panel tilt and snow-shedding calculations.
- Feed the surface area into a roofing cost estimate for material pricing.
What does a 4/12 roof pitch mean?
A 4/12 pitch rises 4 inches for every 12 inches of run — about 18.4 degrees, the most common residential pitch. It sheds rain well, is walkable for maintenance, and has a slope factor of 1.054, so the actual roof area is about 5% more than the floor footprint.
Common mistakes
- Using pitch as the angle. 4/12 is 18.4°, not 4° — they’re different scales.
- Forgetting the slope factor for area. Roofing materials price against sloped surface, not footprint.
- Measuring run as total width. Run is the horizontal distance to the ridge, typically half the span for a gable.
Pitch is the geometry behind the cost side — the roofing cost calculator turns the sloped area into dollars. For the right-triangle math itself, the Pythagorean calculator derives the rafter length.