ROOF PITCH CALCULATOR
How it works
A rise of 48 inches over a run of 96 inches, with a 12-inch overhang.
- Pitch: (48 ÷ 96) × 12 = 6, so the roof is 6/12.
- Angle: arctan(48 ÷ 96) = arctan(0.5) = 26.57°.
- Slope: 48 ÷ 96 × 100 = 50%.
- Rafter to the wall: √(48² + 96²) = 107.33 in.
- Add the overhang: 107.33 + 12 = 119.33 in = 9 ft 11-5/16".
A 6/12 pitch — 26.57°, a 50% slope, and a 9 ft 11-5/16 in rafter including the overhang.
Constants
| Constant | Value |
|---|---|
| Pitch expression | rise per 12 of run |
| Angle from pitch | arctan(rise ÷ run) |
| Rafter multiplier | √(x² + 12²) ÷ 12 |
| Rafter length | √(rise² + run²) + overhang |
SOURCE — roof pitch is stated as rise over a 12-inch run: x/12 = (rise ÷ run) × 12.
SOURCE — the roof angle in degrees is arctan(rise ÷ run); a 6/12 pitch is 26.57°.
SOURCE — pitch x/12 = (rise ÷ run) × 12; angle = arctan(rise ÷ run); roof-area multiplier = √(x² + 12²) ÷ 12.
SOURCE — Pythagoras applied to the rise and the level run, with the overhang added along the same slope.
Quick answers
A 48-inch rise over a 96-inch run is a 6/12 pitch: 26.57 degrees, a 50% slope, and a rafter multiplier of 1.118.
Roof pitch is rise over a 12-inch run, so 6/12 means the roof climbs 6 inches for every 12 inches travelled horizontally.
A 6/12 pitch is 26.57°. To convert any pitch to degrees, take the arctangent of rise divided by run.
Rafter length is √(rise² + run²) plus the overhang — the same Pythagoras that squares a foundation, turned on its side.
The roof-area multiplier for a 6/12 pitch is 1.118, so 1,000 square feet of footprint is 1,118 square feet of roof surface.
FAQ
How do I calculate roof pitch?
Measure the vertical rise over a level 12-inch run and state it as rise/12. If you have the total rise and run instead, pitch = (rise ÷ run) × 12: 48 over 96 is a 6/12 roof.
What is a 6/12 pitch in degrees?
26.57 degrees. The conversion is arctan(6 ÷ 12) = arctan(0.5). A 4/12 roof is 18.43°, an 8/12 is 33.69°, and a 12/12 is exactly 45°.
How do I find rafter length?
Take the square root of rise squared plus run squared, then add the overhang. For a 48-inch rise and a 96-inch run that is 107.33 inches to the wall, or 119.33 inches with a 12-inch overhang.
What is the roof-area multiplier?
√(x² + 12²) ÷ 12, where x is the pitch. It converts the building's footprint into actual roof area: multiply by 1.118 for a 6/12 roof, or 1.202 for an 8/12.
What pitch is considered walkable?
Roofers generally treat anything up to about 6/12 as walkable in good conditions, 7/12 to 9/12 as steep, and 10/12 and above as requiring staging or harnesses. This is judgement, not code.
What is the minimum pitch for asphalt shingles?
Manufacturers commonly permit shingles down to 2/12 with a doubled underlayment, and 4/12 or steeper with standard underlayment. Below 2/12 you need a membrane roof, not shingles. Always confirm with the specific product's instructions.