Knowing your roof’s angle in degrees matters when choosing materials, planning drainage, and meeting building codes. Most roofers talk in pitch (like “4:12”), but many specifications, cut angles, and solar-panel calculators require degrees. This calculator bridges the two instantly.
How to Calculate Roof Pitch in Degrees (Step by Step)
Step One: Identify the rise and run
The rise is the vertical height the roof gains; the run is the horizontal distance it covers. Both must be in the same unit.
Step Two: Divide rise by run to get the slope
slope = rise ÷ run
slope = 4 ÷ 12 = 0.3333
Step Three: Take the arctangent and convert to degrees
The arctangent (inverse tangent) of the slope gives the angle in radians. Multiply by 180/π to get degrees.
degrees = atan(slope) × (180 / π)
degrees = atan(0.3333) × 57.2958
degrees = 18.43°
Step Four: Express as a slope percentage (optional)
slope % = (rise ÷ run) × 100
slope % = (4 ÷ 12) × 100 = 33.3%
Step Five: Normalize to a standard x:12 ratio (optional)
pitch per 12 = (rise ÷ run) × 12
pitch per 12 = (4 ÷ 12) × 12 = 4.00
So a 4:12 pitch equals 18.43° and a 33.3% slope.
What Your Results Mean
| Degrees | Pitch | Typical Use |
|---|---|---|
| 9.5° | 2:12 | Minimum for rolled roofing |
| 18.4° | 4:12 | Standard shingle minimum |
| 33.7° | 8:12 | Steep residential |
| 45.0° | 12:12 | Very steep, cathedral style |
Lower angles shed water more slowly and need underlayment or membrane roofing. Steeper angles shed water and snow quickly but cost more in materials and labor due to the larger surface area.
Tips for Accurate Measurement
Use a 12-inch level and a tape measure against a rafter or the roof deck to get rise and run directly. If you’re measuring from blueprints, the rise and span (total width) are often noted; remember that run is half the span for a symmetric gable roof. Always measure in the same units for both values since the ratio is unitless.