Roof Pitch Calculator
Pitch ratio, angle, and slope percent from rise and run.
Inputs
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Formula
pitch = rise : run; angle = atan(rise/run); slope % = (rise/run) × 100
Roof pitch is expressed as vertical rise per horizontal run (e.g. 4:12). The angle in degrees and slope percent follow from the same rise/run ratio.
Worked example
A 4:12 pitch rises 4 units for every 12 horizontal — about 18.43° or 33.3% slope. Common for residential asphalt shingles where 4:12 is often the minimum for warranty.
Where this can give the wrong answer
- Rise and run can be any consistent units (feet, inches, metres) as long as both match.
- Very low pitch (<2:12) may need membrane roofing, not shingles — codes vary.
- This is pitch geometry only — rafter length needs the hypotenuse (run ÷ cos(angle)).
FAQ
- Under 6:12 is easier to walk; above 8:12 needs roof jacks and harnesses. Pitch doesn't include friction or wet conditions.