Roof Pitch Calculator
Convert roof rise and run into pitch (x-in-12), angle in degrees, slope percent, and the roof-area multiplier used to size shingles and underlayment.
How this calculator works
Roof pitch is the ratio of vertical rise to horizontal run. From those two numbers the calculator derives every way pitch gets expressed — the roofer’s x-in-12 ratio, the angle in degrees, the slope as a percent, and the multiplier used to convert footprint into true roof area.
Formula: Pitch = (rise ÷ run) × 12. Angle = arctan(rise ÷ run). Slope % = (rise ÷ run) × 100. Area multiplier = √(rise² + run²) ÷ run.
Worked example
A roof rising 6 inches over a 12-inch run:
- Pitch: (6 ÷ 12) × 12 = 6-in-12
- Angle: arctan(6 ÷ 12) ≈ 26.6°
- Slope: (6 ÷ 12) × 100 = 50%
- Area multiplier: √(6² + 12²) ÷ 12 ≈ 1.118
Pitch reference
| Pitch | Angle | Area multiplier |
|---|---|---|
| 4/12 | 18.4° | 1.054 |
| 6/12 | 26.6° | 1.118 |
| 8/12 | 33.7° | 1.202 |
| 12/12 | 45.0° | 1.414 |
How to measure
Set a level flat against the roof or a rafter, mark 12 inches, and measure the vertical drop to the surface at that mark. Enter that drop as the rise. Once you have the pitch, use the Roof Area Calculator to turn your footprint into shingle-ready square footage.
Frequently asked questions
What does a 6/12 pitch mean?
It means the roof rises 6 inches for every 12 inches of horizontal run. Roofers express pitch as this rise-over-12 ratio, so a 6/12 roof and a 26.6-degree roof are the same slope stated two different ways.
How do I measure roof pitch without climbing on the roof?
Hold a level horizontally against the roofline (or against a rafter in the attic), mark 12 inches along it, then measure straight down from that mark to the roof surface. That vertical distance is your rise over a 12-inch run — enter it here.
What is the roof-area multiplier for?
A pitched roof has more surface than the flat footprint beneath it. The multiplier — the square root of (rise² + run²) divided by run — is what you multiply the footprint by to get true roof area. A 6/12 roof's multiplier is about 1.118, meaning 12 percent more material than the footprint suggests.
What is considered a steep roof?
Anything above about 9/12 (roughly 37 degrees) is generally called steep-slope and needs extra safety equipment and often more material for waste. Below 3/12 is low-slope and usually needs a membrane rather than standard shingles.
Can I enter a run other than 12?
Yes. The default run is 12 to match the standard pitch convention, but you can enter any rise and run you measured directly and the calculator still returns the correct angle, slope, and multiplier.
Estimates only. Verify quantities with your supplier before purchasing.