Roof Pitch Calculator
Enter the rise and run (or the angle) to get the roof pitch as X:12, the angle in degrees, the grade and the pitch multiplier. Add the building span and footprint to get rafter length and the actual roof area in squares for shingles.
Roof pitch calculator
How to find roof pitch
Pitch is the rise in inches for every 12 inches of horizontal run, written as X:12. Hold a level horizontally against the roof, measure 12 inches along it, then measure straight up to the roof surface: 6 inches means a 6:12 pitch. From any rise and run, pitch = rise ÷ run × 12; the angle is arctan(rise ÷ run).
Pitch multiplier = √(1 + (pitch ÷ 12)²). Multiply the flat footprint by it to get the actual roof surface (1,800 sq ft × 1.118 for 6:12 = 2,012 sq ft, about 20 squares of shingles), and multiply half the span plus overhang by it for the rafter length.
| Pitch | Angle | Grade | Multiplier |
|---|---|---|---|
| 2:12 | 9.46° | 16.7% | 1.0138 |
| 3:12 | 14.04° | 25.0% | 1.0308 |
| 4:12 | 18.43° | 33.3% | 1.0541 |
| 5:12 | 22.62° | 41.7% | 1.0833 |
| 6:12 | 26.57° | 50.0% | 1.1180 |
| 7:12 | 30.26° | 58.3% | 1.1577 |
| 8:12 | 33.69° | 66.7% | 1.2019 |
| 9:12 | 36.87° | 75.0% | 1.2500 |
| 10:12 | 39.81° | 83.3% | 1.3017 |
| 12:12 | 45.00° | 100.0% | 1.4142 |
Common questions
How do I calculate roof pitch?
Divide the rise by the run and multiply by 12. A rise of 4 feet over a run of 8 feet is 6:12.
What angle is a 6/12 roof pitch?
26.57 degrees.
What is the most common roof pitch?
Pitches between about 4:12 and 9:12 are common on US homes.
What is the minimum pitch for asphalt shingles?
2:12, with extra underlayment required between 2:12 and 4:12, per typical manufacturer and IRC rules.
How do I calculate rafter length?
Half the building span (plus overhang) × the pitch multiplier. A 28 ft span at 6:12 with 1 ft overhang: 15 × 1.118 = 16.77 ft.
Sources
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General information, not financial, tax or legal advice. Check important numbers with the official source before acting on them.