Convert roof rise and run into X:12 pitch, angle, slope multiplier, and estimated sloped roof area.
Use any matching small units for rise and run. Horizontal area is the building-footprint projection covered by the roof planes.
pitch = rise ÷ run × 12slope factor = √(rise² + run²) ÷ runsloped area = projected area × slope factorThe sloped area does not include roofing waste. Send it to the roofing calculator to estimate squares and bundles with an appropriate allowance.
Use plans, attic measurements, or safe ground-based methods when possible. Roof work presents serious fall hazards; use qualified professionals and appropriate protective systems.
Pitch6 ÷ 12 × 12 = 6:12
Anglearctan(6 ÷ 12) = 26.57°
Slope factor√(6² + 12²) ÷ 12 = 1.1180
Sloped area1,600 × 1.1180 = 1,788.9 ft² before waste
| Pitch | Angle | Slope factor |
|---|---|---|
| 2:12 | 9.46° | 1.0138 |
| 4:12 | 18.43° | 1.0541 |
| 6:12 | 26.57° | 1.1180 |
| 8:12 | 33.69° | 1.2019 |
| 10:12 | 39.81° | 1.3017 |
| 12:12 | 45.00° | 1.4142 |
The factor converts plan-view area to simple sloped-plane area. Measure dormers, intersecting roofs, and planes with different pitches separately.