Roof Pitch Calculator
Calculate roof pitch from rise and run and instantly convert it to an X:12 pitch, roof angle in degrees, slope percentage, pitch ratio, and rafter length. Use inches, feet, centimeters, meters, or any consistent measurement unit.
Enter Roof Measurements
Enter rise and horizontal run using the same unit.
What Is Roof Pitch?
Roof pitch describes how steep a roof is. In many construction systems, pitch is expressed as the number of vertical units of rise for every 12 horizontal units of run.
For example, a 6:12 roof pitch means the roof rises 6 inches, centimeters, or other equal units for every 12 units of horizontal distance.
What Is Rise?
Rise is the vertical height gained by the roof over a specified horizontal distance. It is the vertical side of the right triangle formed by the roof slope.
What Is Run?
Run is the horizontal distance from the starting point of the roof slope to the point directly below its upper end. For a simple symmetrical gable roof, the run is commonly half the building span.
How to Use the Roof Pitch Calculator
Measure the Rise
Measure the vertical increase from the lower roof point to the upper point.
Measure the Run
Measure the horizontal distance covered over the same section of roof.
Calculate Pitch
The calculator converts rise and run into X:12 pitch, degrees, percentage slope, and rafter length.
How Is Roof Pitch Calculated?
Pitch in X:12 Format
To convert any rise and run measurement into standard roof pitch, divide the rise by the run and multiply by 12: Pitch = (Rise ÷ Run) × 12 .
Roof Angle in Degrees
The roof angle can be calculated using the inverse tangent of the slope: Angle = arctan(Rise ÷ Run) . The result is converted from radians to degrees.
Roof Slope Percentage
Roof slope percentage is calculated as: Slope % = (Rise ÷ Run) × 100 . A 6:12 pitch therefore has a slope of 50%.
Rafter Length
Rise and run form the two shorter sides of a right triangle, so the sloped rafter length is calculated with the Pythagorean theorem: Rafter Length = √(Rise² + Run²) .
Common Roof Pitch Angles
| Roof Pitch | Slope % | Approx. Angle |
|---|---|---|
| 1:12 | 8.33% | 4.76° |
| 2:12 | 16.67% | 9.46° |
| 3:12 | 25% | 14.04° |
| 4:12 | 33.33% | 18.43° |
| 5:12 | 41.67% | 22.62° |
| 6:12 | 50% | 26.57° |
| 8:12 | 66.67% | 33.69° |
| 10:12 | 83.33% | 39.81° |
| 12:12 | 100% | 45° |
Low, Conventional and Steep Roof Pitch
Roof slopes are often described using broad categories. Very low slopes are closer to flat, while larger X:12 values indicate steeper roofs.
| Pitch Range | General Description |
|---|---|
| Below 2:12 | Very low slope |
| 2:12 to below 4:12 | Low slope |
| 4:12 to 9:12 | Conventional / moderate slope |
| Above 9:12 | Steep slope |
How to Calculate Rafter Length from Roof Pitch
The calculator finds the straight-line distance between the two ends of the measured roof slope. This is the hypotenuse of the right triangle formed by rise and run.
For example, with a rise of 6 units and a run of 12 units, the basic rafter length is approximately 13.42 units.
This geometric measurement does not automatically include overhangs, ridge adjustments, birdsmouth cuts, structural details, or other construction allowances.