Roof Pitch Calculator
Use this as a shed roof pitch calculator or lean-to roof pitch calculator when you know the rise and run — or as a roof pitch angle calculator when you only know the angle in degrees. It converts between pitch (X/12), angle, and slope percent, and gives the roof area multiplier.
Pitch is stated against a 12-inch run, e.g. 6/12. The area multiplier turns a flat footprint into true roof area.
Estimates only — not financial advice. This calculator gives approximate figures for planning. It is not financial, tax, or legal advice; check with a qualified professional before making decisions.
How the roof pitch calculator works
Roof pitch is the rise over a standard 12-inch run: a roof that climbs 6 inches for every 12 inches of horizontal run is a 6/12 pitch. This calculator takes rise and run and derives everything else — the angle in degrees (from the arctangent), the slope of the roof as a percentage, and the area multiplier, which is the rafter length divided by the run.
The area multiplier is the practical payoff: multiply your roof’s flat footprint by it to get the true surface area for shingles, metal, or TPO. A 6/12 pitch multiplies area by 1.118; a steep 12/12 doubles the footprint’s math to 1.414.
pitch = rise/12 · angle = atan(rise/run) · slope % = 100 × rise/run · multiplier = √(rise²+run²)/run
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Roof pitch calculator FAQ
What is roof pitch?
Roof pitch is the steepness of a roof, stated as the vertical rise over a 12-inch horizontal run. A 4/12 pitch rises 4 inches per foot of run; 12/12 is a 45-degree roof.
What is a typical shed roof pitch?
Sheds usually sit at 2/12 to 4/12 — low enough for a simple single-slope build, steep enough to shed water. Check your shingle manufacturer: most require at least 2/12, some 3/12 minimum.
What pitch should a lean-to roof have?
Lean-to roofs typically run 1/12 to 4/12. The lower the pitch, the more the roofing choice matters: below 3/12, standing-seam metal or membrane roofing handles water better than shingles.
What is the difference between pitch, angle, and slope?
Pitch is rise per 12 inches of run (6/12), angle is the same slope in degrees (26.6° for 6/12), and slope percent is rise ÷ run × 100 (50% for 6/12). This calculator converts between all three.
How do I measure my roof pitch?
Hold a level horizontally from the roof surface and measure 12 inches along it, then measure straight down from the level to the roof — that drop in inches is your pitch (e.g. 5 inches = 5/12).