Roof Pitch Calculator
Convert roof rise and run into pitch, angle, slope percentage and rafter length.
Formula and sources updated · Data sources · 1View algorithm, constants and default inputs (JSON)
About this calculator
Check local building requirements and the roofing manufacturer instructions for this pitch.
Worked example
calculated with the default values below
Rise 6 in · Run 12 in Pitch (rise per 12 in) 6.00 · Angle 26.57 ° · Slope 50.00 % · Rafter multiplier 1.1180 · Rafter length for this run 13.42 in
Method and assumptions
P = 12r ÷ u; ang = atan(r ÷ u) × 180 ÷ π; L = √(r² + u²) This calculator reports rise/run geometry only. Pitch = rise ÷ run × 12; slope percent = rise ÷ run × 100; rafter length = run × √(rise² + run²) ÷ run. Material suitability and installation requirements depend on local rules and the selected product. Check local building requirements and the roofing manufacturer instructions for this pitch. The references explain definitions and methods; any extra preset must be checked against the assumptions on this page.
Data sources
The references explain definitions and methods; any extra preset must be checked against the assumptions on this page.
Disclaimer
These calculators provide planning estimates only. Building codes, wiring regulations and safety requirements differ by country and change over time, and nothing here replaces a licensed professional or a permit. For structural, electrical or gas work, follow local code and have the installation inspected.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
P = 12r ÷ u; ang = atan(r ÷ u) × 180 ÷ π; L = √(r² + u²)
- r
- Rise (in)
- u
- Run (in)
- P
- Pitch per 12 in run
- ang
- Roof angle (degrees)
- L
- Rafter length over run
This calculator reports rise/run geometry only. Pitch = rise ÷ run × 12; slope percent = rise ÷ run × 100; rafter length = run × √(rise² + run²) ÷ run. Material suitability and installation requirements depend on local rules and the selected product.
Frequently asked questions
How do I use the roof pitch results?
The calculator converts rise and run into pitch, angle, slope percentage and rafter length. It does not decide which roof covering is suitable. Check local requirements and the installation instructions for the specific product. For example, GAF describes special double deck protection for its shingles on 2:12 to less than 4:12 slopes; instructions vary by product.
Which inputs and limits apply to Roof Pitch Calculator?
Use the units shown beside each field. These are form limits, not recommended settings. Rise: 0–120 in; Run: 0.5–240 in P = 12r ÷ u; ang = atan(r ÷ u) × 180 ÷ π; L = √(r² + u²) This calculator reports rise/run geometry only. Pitch = rise ÷ run × 12; slope percent = rise ÷ run × 100; rafter length = run × √(rise² + run²) ÷ run. Material suitability and installation requirements depend on local rules and the selected product. Check local building requirements and the roofing manufacturer instructions for this pitch. The references explain definitions and methods; any extra preset must be checked against the assumptions on this page.
What is a complete worked example for Rise = 6 in; Run = 12 in?
Inputs: Rise = 6 in; Run = 12 in. Calculation: P = 12r ÷ u; ang = atan(r ÷ u) × 180 ÷ π; L = √(r² + u²). Results: Pitch (rise per 12 in) = 6.00; Angle = 26.57 °; Slope = 50.00 %; Rafter multiplier = 1.1180; Rafter length for this run = 13.42 in.