Roofing resources
Roof Pitch Calculator: Ratio, Angle & Multiplier
Convert vertical rise and horizontal run into pitch, angle and a surface-area multiplier.
THE RESULT, EXPLAINED
Clear inputs. Clear results.
Choose your units and calculate to see the result and its assumptions. Changing an input clears the previous result.
What is the formula for roof pitch?
The multiplier is √(1 + (rise ÷ run)²), using the same units for rise and horizontal run. A 6/12 pitch has a multiplier of approximately 1.1180.
How do I calculate roof pitch factor from plan footprint area?
Multiply the horizontal projected roof area by √(1 + (rise ÷ run)²). Include roof overhangs and calculate different facet pitches separately.
For a synthetic example, 2,000 sq ft of projected area at 6/12 becomes 2,236.07 sq ft of sloped area, or 22.3607 roofing squares, before waste.
| Pitch (rise / run) | Area multiplier | Sloped sq ft per 1,000 projected sq ft |
|---|---|---|
| 0/12 | 1.0000 | 1000.00 |
| 3/12 | 1.0308 | 1030.78 |
| 4/12 | 1.0541 | 1054.09 |
| 6/12 | 1.1180 | 1118.03 |
| 8/12 | 1.2019 | 1201.85 |
| 12/12 | 1.4142 | 1414.21 |
When should I use it?
Apply the multiplier to horizontal projected roof area at the matching pitch. Do not apply it to an area already measured along the roof surface. Different facet pitches need separate calculations.