Roof Pitch Calculator
Calculate roof pitch ratio (4:12, 6:12, etc.), angle in degrees, rafter length, and ridge height. Convert between rise/run, degrees, and pitch. Includes roof area multiplier.
in
in
Pitch Ratio
—
Angle (degrees) —
Pitch Category —
Rafter Length Factor —
Extended More scenarios, charts & detailed breakdown ▾
in
in
Pitch Ratio
—
Angle —
Category —
Professional Full parameters & maximum detail ▾
in
ft
ft
in
Pitch & Geometry
Pitch Ratio —
Angle —
Common Rafter Length —
Ridge Height —
Area & Material
Roof Area Multiplier —
Total Roof Area (ft²) —
Hip/Valley Length Factor —
Min Pitch for Asphalt Shingles —
How to Use This Calculator
- Enter rise (inches) and run (inches, default 12).
- Results show pitch ratio, angle in degrees, pitch category, and rafter factor.
- Use Angle to Pitch tab to convert degrees back to pitch ratio.
- Use Rafter Length tab to calculate common rafter length from building span.
- Use the Professional tab for total roof area, hip/valley factors, and material minimums.
Formula
Pitch Ratio = Rise : Run (e.g., 6:12)
Angle = arctan(Rise ÷ Run) in degrees
Rafter Factor = √(Rise² + Run²) ÷ Run
Rafter Length = Rafter Factor × (Span ÷ 2) + Overhang
Example
Example: 6:12 pitch, 30 ft span, 18 in overhang. Angle = arctan(6/12) = 26.6°. Rafter factor = √(36+144)/12 = 1.118. Rafter length = 1.118 × 15 ft + 1.5 ft = 18.3 ft.
Frequently Asked Questions
- A 6:12 pitch means the roof rises 6 inches vertically for every 12 inches of horizontal run. This is a moderate, common pitch for residential homes and equals approximately 26.6 degrees.
- Use a level and measuring tape: place a 12-inch level on the roof surface, measure level, then measure the vertical rise from the 12-inch mark straight down. That rise measurement is your pitch (e.g., 6 inches rise = 6:12).
- Asphalt shingles require a minimum 2:12 pitch (with special underlayment) and work best at 4:12 or greater. Metal roofing can be installed at 1:12. Low-slope roofs under 2:12 typically require TPO, EPDM, or built-up roofing.
- Steeper pitches increase total roof area compared to the footprint. A flat roof has a multiplier of 1.0. A 6:12 pitch adds about 11.8% more area (factor ≈ 1.118). A 12:12 pitch has a factor of 1.414 (41% more area).
- A common rafter runs from the ridge board to the top plate of the wall. Its length = √(rise² + run²) × (run / 12), plus overhang. This calculator shows common rafter length for your span and pitch.