Roof Pitch Calculator
Work out a roof's pitch from rise and run — pitch per 12, slope angle, slope factor, and the roof area from the footprint.
Pitch is the one number every roofing calculation starts from — it turns a flat footprint into a sloped surface. This calculator is pure pitch maths: rise and run in, pitch, angle, factor and area out.
Measure from the ground or the attic. Do not climb the roof to measure it.
Your results
Enter your measurements and press Calculate.
Quantities are rounded up to whole tiles, planks, boxes or bags, after the wastage allowance. Cost appears only when you enter a price.
Formula
All lengths are converted to a single unit before the calculation: 1 ft = 0.3048 m, 1 in = 25.4 mm, 1 ft² = 0.09290304 m², 1 yd² = 9 ft². Material quantities are rounded up — you cannot buy part of a tile, plank or bag.
How to use this calculator
- Measure the rise and the run in the same unit (e.g. inches).
- Enter them above — the pitch, angle and slope factor appear.
- Add the roof footprint if you also want the surface area.
Worked example
| Rise | 6 in |
|---|---|
| Run | 12 in |
| Pitch | (6 ÷ 12) × 12 = 6/12 |
| Slope angle | atan(6 ÷ 12) = 26.57° |
| Slope factor | √(1 + 0.25) = 1.118 |
| Roof area (30 × 40 ft footprint) | 1,200 × 1.118 = 1,341.64 ft² |
Check it by hand: every step above uses the formula in the box. If your numbers match the example inputs but the calculator gives a different answer, please report it via the contact page.
Frequently asked questions
What does 6/12 roof pitch mean?
The roof rises 6 in for every 12 in of horizontal run. It is the standard US way of stating pitch. A 6/12 roof has a slope angle of 26.57° and a slope factor of 1.118 — the roof surface is 11.8% bigger than the footprint.
What is the slope factor?
The number you multiply the footprint by to get the true roof surface area. A 4/12 roof has a factor of 1.054; a 12/12 roof (45°) has a factor of 1.414.
How do I measure roof pitch safely?
From the ground with a level and tape, or from inside the attic on the rafters. Do not climb a roof to measure it — hire a professional for roof access.
What pitch do I need?
That depends on the roofing material and the climate — shingles need at least 2/12, metal can go lower, and snow country needs steeper pitches. Check the manufacturer's minimum and local building codes.
Related calculators
Estimates only. Results are for planning. Measure twice, confirm box coverage and tile sizes on the packaging you buy, and follow the manufacturer's instructions. See the disclaimer.