How to use this calculator
- Measure rise. Vertical inches the roof rises over a 12-inch run.
- Enter run. Default is 12. Change if you're working with a different reference run.
- Add footprint. Optional: enter the building footprint in ft² to get actual roof surface area.
- Read result. Pitch ratio (e.g. 6/12), degrees, percent slope, and roof area in ft² and squares.
Formula
Slope multiplier = √(rise² + run²) / run
Worked example
A 6/12 roof has a 26.57° angle, a 50% slope, and a 1.118 multiplier. A 1,200 ft² footprint becomes 1,342 ft² of roof area, or 13.4 squares of shingles.
Tips for accurate results
- A "square" of roofing equals 100 ft² — order 1.1× your roof area to allow for waste.
- Walkable roofs are typically ≤ 6/12. Steeper roofs need fall-protection gear.
- Most asphalt shingles require at least 2/12 pitch; below that you need a low-slope membrane.