Roof Pitch Calculator
Free roof pitch calculator. Convert between roof pitch (e.g. 6/12), angle in degrees, and slope percentage — plus rafter length from rise and run.
Quick answer
Pitch = rise over run, expressed as a ratio like 6/12 (6 inches of rise per 12 inches of run). 6/12 is moderate; 4/12 is the minimum walkable; 12/12 is a 45-degree slope, very steep. Convert to angle with arctan(rise/run).
Roof Pitch Calculator
Pitch details
How it works
Pitch is expressed as rise per 12 inches of horizontal run. The slope multiplier converts horizontal area to actual roof surface area: √(1 + (rise/12)²). For a 6/12 pitch, every square foot of footprint = 1.118 sq ft of roof. The angle is arctan(rise/12).
When to use it
Estimating shingles or metal roofing (always order based on slope-adjusted area, not footprint), checking if a roof is walkable (anything over 8/12 needs roof jacks), or comparing two house plans.
Common mistakes
Confusing rise/run with degrees. A 12/12 pitch is 45°, not 12°. Roofing material warranties also depend on pitch — most asphalt shingles need at least a 2/12 slope, and many manufacturers void warranty under 4/12 unless you use ice and water shield underneath.
How the roof pitch calculator works
Roof pitch is expressed three ways: as a ratio of rise to 12 inches of run (the U.S. standard, e.g., 6/12), as an angle in degrees (arctan of rise/run, e.g., 26.57° for 6/12), and as a slope percentage (rise ÷ run × 100, e.g., 50% for 6/12). The calculator converts between all three. Rafter length is the hypotenuse: √(rise² + run²) per foot of run.
When to use it
Estimating shingles or roofing material — steeper pitches need more material per square foot of footprint. Computing rafter length for new construction. Translating between architect drawings (often in degrees) and lumber orders (often in pitch ratio). Identifying whether a roof is walkable for inspection or installation (under 6/12 generally yes, over 8/12 needs roof jacks or scaffolding).
Common mistakes
- Confusing pitch and slope. Pitch is rise/run (e.g., 6/12). Slope is rise per total run as a percentage. They describe the same thing in different formats.
- Underestimating shingle material on steeper roofs. A 12/12 roof has ~41% more square footage than its building footprint. Rough rule: multiply ground footprint by 1.0 (4/12), 1.12 (8/12), or 1.41 (12/12) to get roof area.
- Walking on roofs above 6/12 without proper safety. 6/12 is uncomfortable but possible. 8/12 needs roof jacks or harnesses. Above 10/12, scaffolding only.
Frequently asked questions
What's a 6/12 roof pitch in degrees?
About 26.57 degrees. The math: arctan(6/12) = arctan(0.5) = 26.57°. Slope percentage is 50%. The calculator above does all three conversions in one input.
What's the minimum roof pitch?
2/12 is the absolute minimum for asphalt shingles per most manufacturer warranties. Below that, you need a low-slope membrane (TPO, EPDM, or modified bitumen). 4/12 is the comfortable minimum for walkable shingled roofs.
How do I measure roof pitch without climbing on the roof?
From inside the attic, hold a level horizontally against a rafter. Measure the vertical distance from the level's 12-inch mark down to the rafter's underside — that distance in inches is the rise. The pitch is rise/12.