Roof Pitch Calculator
Calculate roof pitch, angle, rafter length and multiplier — works forward and in reverse.
Pitch Ratio
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Angle (degrees)
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Rafter Length (ft)
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Roof Multiplier
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Rise (ft)
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Rafter Length (ft)
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Angle (degrees)
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Common Pitch Reference Table
| Pitch | Angle (°) | Multiplier |
|---|
How the Roof Pitch Calculator Works
Roof pitch is expressed as a ratio of rise to run — the number of inches the roof rises for every 12 inches of horizontal run. This calculator works in two modes. In Mode 1, you enter the actual run and rise in feet; it computes the pitch ratio (rise per 12 inches of run), the angle in degrees using the arctangent, the rafter length using the Pythagorean theorem, and the roof multiplier used for area calculations. In Mode 2, you enter the pitch ratio and run; it back-calculates the rise and rafter length. The pitch reference table shows angles and multipliers for all common pitches from 3/12 to 12/12, letting you quickly look up any standard pitch.
Frequently Asked Questions
What is a 6/12 roof pitch in degrees?
A 6/12 pitch means 6 inches of rise per 12 inches of run. That equals an angle of 26.57°.
How do I measure the pitch of my existing roof?
Hold a level horizontally against the roof. Measure up 12 inches from the roof surface along the level, then measure vertically up to the roof — that's your rise per 12 inches.
What is the minimum roof pitch for shingles?
Most asphalt shingles require a minimum 2:12 pitch. Low-slope applications may need special underlayment or modified bitumen.
How do I calculate rafter length from roof pitch?
Use the Pythagorean theorem: rafter = √(rise² + run²). Or multiply the run by the roof multiplier (e.g. 1.118 for a 6/12 pitch).