Enter the run (half your building's span) and either the rise or the pitch — get pitch, angle, rafter length with overhang, and true roof area for material takeoffs. Imperial and metric.
This tool gives estimates for planning purposes only and isn’t a substitute for professional measurement, a site inspection, or your local building code and supplier guidance. Always verify quantities and code requirements before purchasing materials or beginning work.
Pitch is expressed as rise over a 12-unit run: a 6/12 roof rises 6 inches for every 12 inches you move horizontally. Enter either the pitch or the rise and this tool derives the other, then computes the roof angle in degrees (arctan of rise ÷ run) and the rafter length as the hypotenuse of rise and run, extended along the slope for your overhang.
Worked example: a 12-ft run at 6/12 pitch: rise = 12 × (6/12) = 6 ft. Rafter (no overhang) = √(6²+12²) = 13.4 ft. Angle ≈ 26.6°. With a 12-in overhang, add 12 ÷ cos(26.6°) ≈ 13.4 in ≈ 1.1 ft → total rafter ≈ 14.5 ft.
Shingles, underlayment, and roofing labor are all priced against actual sloped area — not your building's footprint. True area = plan area ÷ cos(angle), so a 6/12 roof needs about 12% more material than the footprint alone suggests; a steeper 9/12 needs about 20% more.
Roof pitch is the rise over a 12-inch run, written as x/12 (e.g. 6/12 means the roof rises 6 inches for every 12 inches of horizontal run). It's the standard way roofing, framing, and shingle warranties describe slope in North America.
Degrees = arctangent(rise ÷ run) × 180/π. A 6/12 pitch works out to about 26.6°. This calculator converts both directions automatically.
Rafter length is the hypotenuse of the rise and run, plus extra length for any overhang measured along the same slope. The formula: √(rise² + run²), then add overhang ÷ cos(angle) for the tail.
A sloped roof has more surface area than the flat footprint below it. True roof area = plan area ÷ cos(pitch angle). A 6/12 roof adds about 12% more area than the footprint — that's the number shingles are actually ordered against.
Under 3/12 is generally low-slope and needs different underlayment and material specs (check manufacturer requirements). Over 9/12 is considered steep and usually requires additional fall protection for anyone working on it.