Roof pitch describes how steep a roof is, in inches of vertical rise per 12 inches of horizontal run (the imperial convention) or as an angle in degrees. The Toolenza calculator converts between rise:run notation, degrees, and percentage grade, and computes the rafter length using the Pythagorean theorem.

Common pitches and what they mean

• Flat / low-slope (0:12 to 2:12, 0–9°) — commercial buildings, modern minimalist homes. Requires special membrane roofing; shingles aren't rated.
• Low (3:12 to 5:12, 14–23°) — ranch houses, sheds. Walkable; cheap to roof.
• Standard (6:12 to 9:12, 27–37°) — most modern residential. The sweet spot for shingle warranties and walkability.
• Steep (10:12 to 12:12, 40–45°) — colonial, Cape Cod, mountain homes. Sheds snow well; harder to roof (requires roof jacks and harnesses).
• Very steep (above 12:12, > 45°) — Gothic, Victorian, A-frames. Sheds everything; treated as a wall for some code purposes.

Why pitch affects every cost

• Material. Steeper roofs have more surface area for the same footprint. A 12:12 roof has ~41% more area than a 4:12 roof over the same floor plan.
• Labour. Anything over 6:12 needs harnesses and slows installation significantly.
• Underlayment. Codes require ice-and-water shield up to 24 inches past the heated wall on low slopes; steep roofs need different underlayment.
• Shingle warranty. Below 4:12, asphalt shingles need a double underlayment for warranty coverage. Below 2:12, they aren't rated at all.

Pitch and rafter length

Given span (full width of building) and pitch, the rafter length is √(run² + rise²) where run = span/2 and rise = run × (pitch_rise/pitch_run). A 30-ft-wide building with 6:12 pitch has run = 15 ft, rise = 7.5 ft, rafter = 16.77 ft. Always add 12–18 inches for overhang and birdsmouth.