The roofing toolkit
Roof Pitch Calculator
Use rise and horizontal run to calculate roof pitch, roof angle in degrees, slope percentage, and surface area factor.
Enter any measurement
Edit rise/run, degrees, or percent. All three stay in sync.
Area viewed from above, for roof planes sharing this pitch.
Roof pitch
conventional4:12
Angle
18.4°
Slope
33.33%
Standard pitch: inches of rise per 12 inches of run.
Area multiplier 1.054×
How to use this calculator
- Enter the vertical rise and horizontal run in inches, or enter an angle or slope percentage. The other fields update as you type.
- The result always uses a 12-inch run. For example, 8 inches of rise over 24 inches of run becomes 4:12, 18.4°, and 33.33%.
- Optionally enter the roof’s horizontal projected area in square feet. Surface area = projected area ÷ cos(angle). For mixed pitches, calculate each section separately. This excludes waste and material allowance.
Angles must be at least 0° and less than 90°. A 90° surface is vertical and has no finite x:12 roof pitch. Measurements are calculated at full precision; displayed results are rounded.
About the slope labels
This calculator uses asphalt-shingle application bands: flat (including very low slope) below 2:12; low slope from 2:12 to below 4:12; conventional from 4:12 through 21:12; steep slope above 21:12. These descriptive labels are not a roof-access safety classification.
“Flat” below 2:12 is this tool’s grouping. Follow the roofing manufacturer’s instructions for material suitability and installation.
Sources: ARMA Residential Asphalt Roofing Manual, page 17 and ARMA steep-slope guidance.
A few helpful answers
Roof pitch, explained
What does a 6/12 roof pitch mean?
A 6/12 pitch means the roof rises 6 inches for every 12 inches of horizontal run. Its angle is approximately 26.6 degrees.
Is run the same as the full width of a roof?
No. Run is the horizontal distance for the slope you are measuring, not the distance along the roof. For a simple, symmetrical gable roof, one side’s run is half the total span.
How do I know my roof pitch?
Check a roof measurement report, or measure from a safely accessible attic. Hold a level horizontally under a rafter and measure its vertical rise over 12 inches of run. A 4-inch rise means a 4/12 pitch. For a different run, divide rise by run and multiply by 12.
What is the most common roof pitch?
Most U.S. residential roof slopes fall between 4/12 and 9/12, according to GAF. The pitch of an individual home varies with its design, so measure your own roof rather than assuming a typical pitch.
What is a 4/12 roof pitch in degrees?
A 4/12 roof pitch is approximately 18.4 degrees, calculated as arctan(4 ÷ 12). It rises 4 inches for every 12 inches of horizontal run and has a slope of about 33.33%.