Roof Pitch Calculator
Slide to your pitch and get the multiplier, roof angle, and the surface area it adds — plus the full factor chart from 1/12 to 18/12.
Pitch multiplier chart (1/12 – 18/12)
| Pitch | Multiplier | Angle | Surface per 1,000 ft² footprint |
|---|---|---|---|
| 1/12 | 1.003 | 4.8° | 1,003 ft² |
| 2/12 | 1.014 | 9.5° | 1,014 ft² |
| 3/12 | 1.031 | 14.0° | 1,031 ft² |
| 4/12 | 1.054 | 18.4° | 1,054 ft² |
| 5/12 | 1.083 | 22.6° | 1,083 ft² |
| 6/12 | 1.118 | 26.6° | 1,118 ft² |
| 7/12 | 1.158 | 30.3° | 1,158 ft² |
| 8/12 | 1.202 | 33.7° | 1,202 ft² |
| 9/12 | 1.250 | 36.9° | 1,250 ft² |
| 10/12 | 1.302 | 39.8° | 1,302 ft² |
| 11/12 | 1.357 | 42.5° | 1,357 ft² |
| 12/12 | 1.414 | 45.0° | 1,414 ft² |
| 13/12 | 1.474 | 47.3° | 1,474 ft² |
| 14/12 | 1.537 | 49.4° | 1,537 ft² |
| 15/12 | 1.601 | 51.3° | 1,601 ft² |
| 16/12 | 1.667 | 53.1° | 1,667 ft² |
| 17/12 | 1.734 | 54.8° | 1,734 ft² |
| 18/12 | 1.803 | 56.3° | 1,803 ft² |
How to use the multiplier in a bid
Measure or pull the roof's footprint (the flat area the roof covers), multiply by the pitch factor above, then add a waste factor — typically 10–15% for a standard roof and more for complex, cut-up roofs — and divide by 100 to get squares. Footprint 2,400 ft² at 8/12: 2,400 × 1.202 = 2,885 ft², plus 12% waste = 3,231 ft² ≈ 32.3 squares ≈ 97 bundles.
Or skip the manual math: use the squares calculator — or pull the footprint, pitch, and squares straight from satellite with an instant Rooftops AI roof report.
FAQ
What is a roof pitch multiplier?
The pitch multiplier (or pitch factor) converts a roof's flat footprint area into its actual sloped surface area. It equals the square root of ((rise ÷ 12)² + 1). A 2,000 sq ft footprint at 6/12 pitch has 2,000 × 1.118 = 2,236 sq ft of actual roof surface.
How do I figure out my roof's pitch?
Measure how many inches the roof rises over 12 inches of horizontal run — from a ladder at the eave, in the attic against a rafter, or with a phone level app. A roof that rises 6 inches per foot of run is a 6/12 pitch. Satellite measurement tools like Rooftops AI estimate pitch remotely from imagery.
What pitch is considered walkable?
Most crews treat up to 6/12 as comfortably walkable, 7/12–9/12 as steep (chicken ladders, more caution, often a steep charge), and 10/12+ as requiring harnesses and staging. Steeper pitches also add labor cost and waste to a bid.
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