Roof pitch calculator
- Pitch
- 6:12
- Angle
- 26.57°
- Slope
- 50%
- Ratio
- 1 : 2
- Pitch factor
- 1.118
- Rafter (for run)
- 13.416 ft
Change any field; the others update.
The formulas
Pitch compares vertical rise with horizontal run. Every format is the same ratio written differently:
- x:12 = rise ÷ run × 12
- Degrees = tan⁻¹(rise ÷ run)
- Percent = rise ÷ run × 100
- Rafter length = run × √(1 + (rise ÷ run)²), measured along the slope from wall line to ridge, before overhang
Roof pitch chart: x:12 to degrees
| Pitch | Degrees | Percent | Pitch factor |
|---|---|---|---|
| 1:12 | 4.76° | 8.3% | 1.0035 |
| 2:12 | 9.46° | 16.7% | 1.0138 |
| 3:12 | 14.04° | 25.0% | 1.0308 |
| 4:12 | 18.43° | 33.3% | 1.0541 |
| 5:12 | 22.62° | 41.7% | 1.0833 |
| 6:12 | 26.57° | 50.0% | 1.1180 |
| 7:12 | 30.26° | 58.3% | 1.1577 |
| 8:12 | 33.69° | 66.7% | 1.2019 |
| 9:12 | 36.87° | 75.0% | 1.2500 |
| 10:12 | 39.81° | 83.3% | 1.3017 |
| 11:12 | 42.51° | 91.7% | 1.3566 |
| 12:12 | 45.00° | 100.0% | 1.4142 |
Values are calculated from the formulas above, not looked up, and rounded to the decimals shown. For what each pitch means in practice and how to measure a roof, read roof pitch angles explained. Planning a loft conversion? The stair calculator and room area calculator help with the next steps.
Questions
How do I convert a 6:12 roof pitch to degrees?
Divide the rise by the run (6 ÷ 12 = 0.5) and take the arctangent: tan⁻¹(0.5) = 26.57°. The same pitch is a 50% slope.
What does 4:12 pitch mean?
The roof rises 4 units for every 12 units of horizontal run. It works in any unit: 4 inches per foot, or 333 mm per meter. It is 18.43° or a 33.3% slope.
How do I calculate rafter length from pitch?
Multiply the horizontal run by the pitch factor, √(1 + (rise ÷ run)²). For a 6:12 roof the factor is 1.118, so a 4 m run needs a 4.47 m rafter before overhang.
Is roof pitch the same as roof slope?
Both words describe how steep a roof is, and the same steepness can be written three ways: as rise in 12 (x:12), in degrees, or as a percentage (rise ÷ run × 100). This calculator converts between all three.