Roof Pitch Calculator
Calculate roof pitch in degrees, as a rise/run ratio, or as a percentage. Enter any one value and the calculator converts instantly. Includes pitch factor for surface area. Free, no signup.
Rafter / Hip & Valley
Calculate rafter and hip/valley lengths from pitch and span
Plan-view distance from wall to ridge (one rafter)
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Roof pitch — did you know?
What exactly is roof pitch?
Roof pitch is the steepness of a roof, expressed as an angle in degrees or as a ratio of rise to run. UK uses degrees (e.g. 35°). US uses rise/run (e.g. 6:12 = 6 inches rise per 12 inches run). Both describe the same thing.
Degrees vs ratio conversion
To convert ratio to degrees: pitch° = arctan(rise ÷ run). A 6:12 roof = arctan(0.5) = 26.57°. To convert degrees to ratio: tan(pitch°). At 35°, tan(35) = 0.700, so the ratio is ~7:10.
Why pitch matters for materials
Pitch determines roof surface area. The pitch factor (1 ÷ cos(pitch°)) converts plan area to actual roof area. At 35°, the factor is 1.221 — 100 m² plan becomes 122.1 m² of roof surface.
Minimum pitch by material
Concrete/clay tiles need 17.5°+ in UK; metal standing seam 3°+; slate 20°+; felt/membrane flat roofs need 1:80 fall (~0.7°). Below minimums, water ponds and penetrates.
Formulas used
Pitch from rise/run
pitch° = arctan(rise ÷ run)
Rise/run from pitch
ratio = tan(pitch°)
Pitch as percentage
percent = (rise ÷ run) × 100
Pitch factor
factor = 1 ÷ cos(pitch°)
Frequently asked questions
How do I calculate roof pitch in degrees?
Measure rise over a known run (e.g. 300mm over 1000mm) and calculate arctan(0.3) = 16.7°. Or use a digital level on the roof surface.
What is a 6:12 pitch in degrees?
arctan(6/12) = 26.57°. One of the most common US residential roof pitches.
What pitch factor should I use?
1 ÷ cos(pitch°). At 25° = 1.103, at 35° = 1.221, at 45° = 1.414. Multiply plan area by this factor for actual roof surface area.
What is the best free roof pitch calculator?
One that converts between degrees, ratios, and percentages, and shows the pitch factor. This tool does all of that, free with no signup.