Roof pitch calculator
From rise and run to the right roof angle.
Pitch preview
Section AHave rise and run?
Use the same unit for both measurements.
The math behind the angle
Angle = arctan(pitch ÷ 12)
Area factor = √(1 + (pitch ÷ 12)²)
Use horizontal run, not the sloped rafter length. A 6:12 pitch is a 50% slope and a 26.6° angle.
Use this pitch in your roof planCalculation breakdown — every section
Building lengths in ft; areas in sq ft. Overhang is horizontal and added on both ends of each dimension. Calculations use unrounded values; displayed figures may not add exactly.
| Section / shape | Wall dimensions | Overhang per side | Roof footprint | Pitch / multiplier | Surface area / share |
|---|---|---|---|---|---|
| Section Agable | 40.00 × 30.00 ft | 1.00 ft | 42.00 × 32.00 ft1,344.00 sq ft | 6.00:12× 1.11803 | 1,502.64 sq ft100.00% of total |
- Surface area before waste
- 1,502.64 sq ft
- Waste allowance (10%)
- 150.26 sq ft
- Order area including waste
- 1,652.90 sq ft · 16.53 roofing squares
Independent rectangular sections only. Overlaps, shared edges and valleys are not automatically deducted or constructed. Hip sections require equal pitch on every face. Confirm joined-roof measurements separately.
Package quantities round up after waste. Current assumptions: shingles 33.33 sq ft/bundle; underlayment 400.00 sq ft effective coverage/roll; cap 25.00 ft/bundle. These product settings use feet even when geometry is displayed in meters. Match the packaging and manufacturer’s overlap instructions before ordering.
Planning estimate only. Excludes labor, tax, removal, delivery, starter strips, flashing, ventilation, fasteners and deck repairs.
Calculation breakdown — every section
Building lengths in ft; areas in sq ft. Overhang is horizontal and added on both ends of each dimension. Calculations use unrounded values; displayed figures may not add exactly.
| Section / shape | Wall dimensions | Overhang per side | Roof footprint | Pitch / multiplier | Surface area / share |
|---|---|---|---|---|---|
| Section Agable | 40.00 × 30.00 ft | 1.00 ft | 42.00 × 32.00 ft1,344.00 sq ft | 6.00:12× 1.11803 | 1,502.64 sq ft100.00% of total |
- Surface area before waste
- 1,502.64 sq ft
- Waste allowance (10%)
- 150.26 sq ft
- Order area including waste
- 1,652.90 sq ft · 16.53 roofing squares
Independent rectangular sections only. Overlaps, shared edges and valleys are not automatically deducted or constructed. Hip sections require equal pitch on every face. Confirm joined-roof measurements separately.
Package quantities round up after waste. Current assumptions: shingles 33.33 sq ft/bundle; underlayment 400.00 sq ft effective coverage/roll; cap 25.00 ft/bundle. These product settings use feet even when geometry is displayed in meters. Match the packaging and manufacturer’s overlap instructions before ordering.
Planning estimate only. Excludes labor, tax, removal, delivery, starter strips, flashing, ventilation, fasteners and deck repairs.
Example arithmetic checked October 28, 2026 against independent geometry reference cases. Measurement method. This is a software calculation check, not a professional roof survey.
Understanding roof pitch, angle and slope
Roof pitch is expressed here as rise for every 12 units of horizontal run. It is a ratio, so 6 inches over 12 inches and 50 centimeters over 100 centimeters describe the same slope.
Is 6:12 the same as 6 degrees?
No. A 6:12 pitch means a rise equal to half the horizontal run. Its angle is about 26.6 degrees.
How do I convert degrees to pitch?
Multiply the tangent of the angle by 12. For example, tan(45°) × 12 = 12, so a 45-degree roof has a 12:12 pitch.
Can this calculate structural rafter lengths?
This calculator estimates slope and surface area only. Structural rafter sizing, load capacity, ridge details and cutting allowances require a separate design.
How should I measure the roof?
Use existing plans or measurements taken from a safe, accessible position. You do not need to climb onto a roof to use this calculator.
Roof pitch conversion table
Pitch is rise per 12 units of horizontal run. Slope percentage is rise ÷ run × 100; angle is arctan(rise ÷ run). The area factor converts horizontal roof footprint into sloped roof area.
| Pitch | Angle | Slope | Area factor |
|---|---|---|---|
| 2:12 | 9.46° | 16.67% | 1.0138 |
| 3:12 | 14.04° | 25.00% | 1.0308 |
| 4:12 | 18.43° | 33.33% | 1.0541 |
| 5:12 | 22.62° | 41.67% | 1.0833 |
| 6:12 | 26.57° | 50.00% | 1.1180 |
| 7:12 | 30.26° | 58.33% | 1.1577 |
| 8:12 | 33.69° | 66.67% | 1.2019 |
| 9:12 | 36.87° | 75.00% | 1.2500 |
| 10:12 | 39.81° | 83.33% | 1.3017 |
| 12:12 | 45.00° | 100.00% | 1.4142 |
Example: 18 inches of rise over 36 inches of run
18 ÷ 36 × 12 = 6, so the pitch is 6:12. Its slope is 50%, its angle is approximately 26.57°, and its area factor is approximately 1.1180. The same ratio works with centimeters or any other consistent length unit.
Converting an angle back to pitch
Pitch per 12 = tan(angle) × 12. Use degrees mode if calculating by hand. A 45° angle corresponds to a 12:12 pitch, a 100% slope, and an area factor of about 1.4142. Run is the horizontal distance, not the distance along the sloped roof.
Method: geometric roof planning estimates. Updated September 27, 2026. Verify measurements and product specifications before ordering.