Roofers speak in twelfths: a 6/12 pitch climbs six inches for every horizontal foot. This calculator translates any rise/run pair into that language — plus the degrees, the rafter length, and the honest answer about walking on it.
Reading the numbers
6/12 is 26.6°, a 50% grade, and needs 13.42 inches of rafter per foot of run (Pythagoras: √(6² + 12²)). A total run of 14 feet therefore wants rafters of 14 × 13.42 ÷ 12 ≈ 15.7 ft before overhangs. The diagram redraws to scale so a 3/12 looks shallow and a 12/12 looks like the 45° it is.
Walkability, honestly
Up to 6/12 most people can walk with care and grippy soles. 7/12–9/12 is experienced-footing territory. Past 10/12, professionals stage or harness — and insurance rates for roofing work step up around 8/12 for good reason. The verdict line applies these commonly used thresholds.
Pitch drives materials
Below 2/12, shingles can't shed water fast enough — membrane or metal territory. 2/12–4/12 needs upgraded underlayment per manufacturer specs. Steeper pitches shed better, last longer, and cost more to build and roof: more rafter, more sheathing, more shingles per plan-footprint — the rafter multiplier is exactly that materials factor.
Related trades math
The same right-triangle runs the stair calculator (rise/run at human scale) and the triangle calculator (the general case). Roof area for shingles = plan area × the rafter multiplier ÷ 12 — get plan area from the square footage calculator.
Reference guidance; manufacturer specs and local code govern.