FixerCalc

Roof Pitch Calculator

Roofers talk in pitch (6:12). Architects may use degrees. Takeoffs use a multiplier. This calculator shows all three from the same rise and run.

Last reviewed 2026-08-25. How we calculate

Results update as you type. Units stay imperial inside the math.

Triangle

Vertical change. Use the same unit system as run (inches is standard in the US).

Horizontal change. A 12-inch run is the usual US convention.

Results

  • Pitch

    6.0:12

  • Angle

    26.6°

  • Area / rafter factor

    1.1180

  • Slope

    50.0%

  • Rafter length per same-unit run

    13.42

    If run is 12 in, this is rafter inches per 12 in of run.

  • Measure rise and run on the rafter or a level and tape—not from a ground photo if you need to order materials.
  • Some codes and shingle warranties have maximum pitches. Check the product, not only this number.

How this calculation works

  1. Pitch in US practice is inches of rise per 12 inches of run: (rise/run) × 12 : 12.
  2. Slope percent is (rise/run) × 100. That is not the same as pitch; a 6:12 roof is a 50% slope.
  3. The area factor is the rafter-length ratio √(1 + (rise/run)²). Multiply plan area by this factor for sloped surface area.

pitch = (rise/run)×12 : 12; degrees = arctan(rise/run); factor = √(1 + (rise/run)²)

What to do next

  • Use the factor in the roof area calculator rather than guessing living-area square footage.
  • If you only know degrees (from a drawing), convert: rise/run = tan(angle).
  • Confirm whether “flat” roofs in your market still have a 1/4:12 or 1/2:12 drainage slope.

FAQ

Is 6/12 the same as 6:12?
Yes. Both mean 6 inches of rise for every 12 inches of run. Avoid writing 6/12 if it could be read as a fraction of a foot.
Can I enter rise and run in feet?
Yes, as long as both fields use the same unit. The ratios cancel. The labels say inches because that is how most US tapes are used on rafters.

Sources

  • Pitch X:12 = (rise/run)×12; angle = arctan(rise/run); factor = √(1 + (rise/run)²)

Cost defaults are typical US planning bands, last reviewed 2026-08-25. Edit the price fields on this page rather than treating them as a local market index.