Roof Slope Calculator
Enter your roof's rise and run to get the pitch ratio, percent slope, angle in degrees, and slope category in an instant.
What your result means
The pitch ratio is the shorthand roofers use (rise:run). The percent slope and degree angle say the same thing in two other forms, and the slope category tells you which roofing materials will work. Anything under 4:12 is low slope and needs a membrane, the 4:12 to 9:12 range is conventional shingle territory, and steeper than that means harness-and-staging work.
How to use this calculator
- Measure the rise (vertical height) of your roof in inches using a level on a rafter or a measurement from the gable end.
- Use 12 inches as the run for standard pitch notation.
- Enter both values in the calculator above.
- Read the pitch ratio, percent slope, angle in degrees, and slope category.
- Compare to your roofing material's minimum pitch requirement.
The formula
Slope is just rise over run. Divide the rise by the run and multiply by 100 for percent slope, or take the arctangent of rise over run for the angle in degrees. The pitch ratio is simply the two numbers written as rise:run.
Worked example
Say your roof rises 6 inches for every 12 inches of run. Enter 6 for Rise and 12 for Run. You'll get a 6:12 ratio, 50% slope, about a 26.6 degree angle, and a Conventional slope reading. That pitch handles asphalt shingles, metal panels, and most tile.
Common roof pitches
| Pitch | Percent slope | Angle | Category |
|---|---|---|---|
| 2:12 | 16.7% | 9.5° | Low slope |
| 3:12 | 25.0% | 14.0° | Conventional |
| 4:12 | 33.3% | 18.4° | Conventional |
| 6:12 | 50.0% | 26.6° | Conventional |
| 8:12 | 66.7% | 33.7° | Conventional |
| 9:12 | 75.0% | 36.9° | Steep slope |
| 12:12 | 100.0% | 45.0° | Steep slope |
Tips & gotchas
- Below 4:12, standard shingles won't shed water fast enough. You'll need a low-slope membrane like TPO, EPDM, or modified bitumen.
- Once you're past 9:12 you're working steep, so plan on fall protection and harnesses.
- The 12 in "X:12" is just a convention, not a real measurement. Any run length works as long as you keep it consistent.
- Measure your pitch twice before you buy materials. Get it wrong and your overhang and trim numbers go with it.
- A steep roof has more surface than its footprint, so don't order shingles off the building's square footage alone.
Frequently asked questions
What pitch is normal for a residential roof?
Most US homes land between 4:12 and 9:12. That range covers asphalt shingles, metal, and tile.
Can I measure roof pitch without going on the roof?
Yes. Put a level on a visible rafter in the attic, or measure off the gable end if you can reach it.
What is the steepest practical roof pitch?
12:12, which is 45 degrees, is the steepest standard residential pitch. Anything steeper is rare and needs special framing.
Does roof pitch affect material cost?
It does. A steeper roof has more surface area than the footprint, so it eats more shingles, underlayment, and labor.
Will this work for metal roofing too?
Yes. The pitch ratio is the same across materials. Just check your metal panel's minimum pitch with the manufacturer before you commit.
Related calculators
Estimates only — see our full disclaimer.