About the Roof Pitch Calculator
Roof pitch is communicated as rise : run — typically per 12 units of horizontal distance. A 6:12 pitch rises 6 inches for every 12 inches of run, equivalent to ~26.6°.
Standard pitch classes
- Flat: 0–2:12 (0–9.5°) — usually torch-on or single-ply membrane
- Low slope: 2:12–4:12 (9.5–18.4°) — special low-slope shingles or metal
- Conventional: 4:12–9:12 (18.4–36.9°) — most domestic homes
- Steep: 9:12–21:12 (36.9–60°) — common in alpine and historic roofs
Rafter length
Rafter length = √(rise² + run²). Add the eave overhang to get the total cut length.
Frequently Asked Questions
How do I measure pitch from outside? Hold a 12-inch level horizontally against the roof, measure the vertical distance from the level's free end down to the roof — that's your rise per 12.
What pitch do I need for snow? 6:12 or steeper is common in snow regions to encourage shedding. Below 4:12, snow tends to accumulate.
Important Note: Always consult a structural engineer or qualified roofer before specifying or modifying a roof.
Related Calculators
- Concrete Calculator — Volume of concrete needed for slabs, footings, columns and post holes. Cubic metres, cubic yards and bag count.
- Tile, Paint & Flooring Calculator — Tiles, litres of paint or boxes of flooring needed for any room — with built-in waste allowance.
- Square Footage Calculator — Floor or land area for rectangles, triangles, circles and trapezoids. Converts m², ft², yd², acres and hectares.