Roofing & Gutters
Roof Pitch Calculator
Enter how many inches the roof rises over a measured horizontal run. You get the pitch written the way roofers say it (6 in 12), the angle in degrees, the slope percent, and the area factor used to size the roof surface.
Worked example
- Pitch = rise / run x 12 = 6 / 12 x 12 = 6 in 12.
- Angle = arctan(6 / 12) = 26.6 degrees.
- Area factor = square root of (12^2 + 6^2) / 12 = 1.118: multiply the flat footprint by it to get the roof surface.
Common sizes at a glance
| Size | Pitch | Angle | Slope |
|---|---|---|---|
| 3/12 | 3 in 12 | 14 degrees | 25% |
| 4/12 | 4 in 12 | 18.4 degrees | 33.3% |
| 5/12 | 5 in 12 | 22.6 degrees | 41.7% |
| 6/12 | 6 in 12 | 26.6 degrees | 50% |
| 7/12 | 7 in 12 | 30.3 degrees | 58.3% |
| 8/12 | 8 in 12 | 33.7 degrees | 66.7% |
| 9/12 | 9 in 12 | 36.9 degrees | 75% |
| 10/12 | 10 in 12 | 39.8 degrees | 83.3% |
| 12/12 | 12 in 12 | 45 degrees | 100% |
Three ways to find rise and run
From the attic is the safest. Hold a level against the bottom of a rafter, mark a point 12 in along the level, and measure straight up from that mark to the rafter. That vertical number is the rise per 12.
From the ground, you can measure a gable end. The run is half the building width and the rise is the height from the top plate to the ridge. Enter any run, it does not have to be 12; the tool scales it.
- Attic: level plus tape on the underside of a rafter
- Gable end: half the width as run, wall top to peak as rise
- Phone level apps: read the angle, then compare with the table
Reading pitch, angle and percent
Pitch, angle and slope percent describe the same roof in different units. A 6 in 12 roof climbs 6 in for every foot it moves inward, which is a 26.6 degree angle and a 50% slope. A 12 in 12 roof is 45 degrees.
Shingle and panel makers list a minimum pitch for their product, and steeper roofs need extra care to walk. Most product sheets use the in-12 form, so that is the number to carry with you.
The area factor is the useful part
A sloped roof has more surface than the flat footprint under it. The area factor tells you how much more: 1.118 at 6 in 12. Multiply the footprint, overhangs included, by that factor to get roof area, or let the roof square footage calculator do it.
The same number, read as feet, is the rafter length per foot of run. That is the start of the rafter length calculator, which also handles the ridge board and the overhang.
Low slopes and steep slopes
Very low pitches shed water slowly and may need a different roofing product or extra underlayment. Steep pitches use more material per square foot of house and are slower to install. Roofing products and the local building code set the limits, and a licensed professional has the final word on any roof work.
Questions
What angle is a 4/12 roof pitch?
About 18.4 degrees, a 33.3% slope. An 8/12 pitch is about 33.7 degrees.
Is pitch the same as slope?
People use the words loosely. Here, pitch means rise per 12 in of run, and slope means the same ratio written as a percent.
Can I measure pitch from a photo?
Only roughly. Camera angle distorts lines, so confirm with a level and tape at the rafter or gable end before you order materials.
How this works: formulas and typical values are listed on our method page; every data source and its license is on sources.
Last reviewed November 2026.