Roof Pitch Calculator
Calculate roof pitch, angle, and rafter length from rise and run.
Roof Pitch Calculator
What This Calculator Does
The Roof Pitch Calculator computes the slope, angle in degrees, and rafter length per foot of run from your roof's rise and run measurements. Enter the rise (vertical increase in inches) over a standard 12-inch run to get the roof pitch ratio, angle, and rafter multiplier.
Roof pitch determines which roofing materials you can use, affects attic space, and influences cost. A low-slope roof (2/12 to 4/12) is common on modern homes and can use standard asphalt shingles. A steep roof (8/12 or higher) requires specialized installation and more materials - increasing cost by 15-40% compared to a low slope. The rafter multiplier is essential for converting attic floor area to actual roof surface area for material ordering.
Standard US residential roof pitches range from 3/12 (low) to 9/12 (steep). Common is 4/12 to 6/12. Enter your rise measurement and the calculator returns everything needed to quote roofing materials.
How to Use
- Measure the roof rise: from the top of the wall plate, measure vertically to the underside of the ridge board or rafter at a point 12 inches horizontally from the edge.
- Alternatively, use a pitch gauge app or speed square directly on an existing rafter.
- Enter the rise in inches into the field (for a 4/12 pitch, enter 4). The run defaults to 12 inches.
- Click "Calculate" to get the pitch ratio, angle in degrees, and rafter length per 12 inches of run.
- Multiply the rafter length per foot by the total run to get full rafter length for material ordering.
Reference Table
| Pitch (X:12) | Angle (deg) | Rafter/ft | Area Multiplier | Common Use |
|---|---|---|---|---|
| 2:12 | 9.5deg | 12.2 in | 1.02 | Low-slope, flat roof |
| 4:12 | 18.4deg | 12.7 in | 1.05 | Standard residential |
| 6:12 | 26.6deg | 13.4 in | 1.12 | Moderate slope |
| 8:12 | 33.7deg | 14.4 in | 1.20 | Steep, Victorian |
| 10:12 | 39.8deg | 15.6 in | 1.30 | Very steep |
| 12:12 | 45.0deg | 17.0 in | 1.42 | Maximum steep |
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