CarpentryInstant Tool
Roof Pitch Calculator
Convert roof rise and run into pitch e.g. 6 or 12, angle in degrees, rafter length, and slope multiplier.
inches
ft
inches
Preset Standard Pitches:
How Roof Pitch Calculator Works
Pitch = Rise / 12 in | Pitch Angle = arctan Rise divided by 12 × 180 / π | Slope Factor = Square Root of 1 plus Rise over 12 squaredIn the United States, roof pitch is designated as inches of vertical rise per 12 inches of horizontal run e.g. 6:12 pitch rises 6 inches for every foot of run. The pitch factor is used by roofers to multiply flat footprint area to find actual sloped surface area.
Variable Breakdown
Rise
Vertical RiseInches of rise per 12 inches of horizontal run
Run
Horizontal RunHorizontal span from outer wall to ridge in feet
Factor
Slope FactorMultiplier = Square Root of 1 plus Rise over 12 squared
Angle
Pitch AngleIncline angle in degrees = arctan - Rise / 12
Example Calculation
Gable Roof Rafter Calculation
A ranch home with 6:12 pitch, a 16-foot horizontal run, and 12-inch overhang.
- Calculate slope angle: arctan 6 over 12 = 26.57 degrees.
- Calculate slope factor: Square Root of 1 plus 0.5 squared = 1.118.
- Calculate base rafter length: 16 ft × 1.118 = 17.89 ft.
- Add 12 inch overhang: 17.89 ft + 1.12 ft = 19.01 ft.
Result:26.57° Pitch - 1.118 Slope Factor, 19.01 ft Rafter
Standard Roof Pitches, Angles and Materials
| Pitch Ratio | Angle in Degrees | Slope Factor | Allowed Roofing Material |
|---|---|---|---|
| 2:12 Flat Slope | 9.46° | 1.014 | Built-up or Rubber Membrane |
| 4:12 Low Slope | 18.43° | 1.054 | Asphalt Shingles with Double Underlayment |
| 6:12 Conventional | 26.57° | 1.118 | Standard Asphalt Shingles or Metal |
| 8:12 Moderate Slope | 33.69° | 1.202 | All Shingles, Metal, Tile, or Slate |
| 12:12 Steep Slope | 45.00° | 1.414 | Architectural Shingles, Slate, or Tile |
Frequently Asked Questions
What is a 6:12 roof pitch in degrees?
A 6:12 roof pitch corresponds to an angle of 26.57 degrees, with a slope factor multiplier of 1.118.
What is the minimum roof pitch for asphalt shingles?
The minimum standard pitch for standard asphalt shingles is 2:12 with double underlayment, and 4:12 for standard underlayment application. Pitches below 2:12 require flat-roof membranes.
What is considered a steep pitch roof?
Pitches between 4:12 and 8:12 are conventional, while pitches of 9:12 and above are considered steep slopes requiring safety harnesses and roofer jacks.
How do you find roof pitch with a level and tape measure?
Place a 12-inch level horizontally from your roof surface. Measure the vertical distance in inches from the 12-inch mark down to the roof. That measurement is your rise over 12.
What is a roof square in roofing estimates?
One roofing square equals 100 square feet of roof surface area. For example, a 2400 sq ft roof equals 24 squares of shingles.
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