Roof Pitch Calculator

Your details

Switch all lengths between inches/feet and centimetres/metres.
Vertical height the roof gains over the run. Use the same unit as the run.
in
Horizontal distance the rise spans. Use 12 to read the pitch directly as x:12.
in
Currency
Roof pitchConventional pitch
4:12

Rise per 12 units of run

Slope angle18.43°
Grade33.3%
Slope factor1.0541
Rafter (line) length12.65 in
Rise per 124
4 :12
Flat<2Low2-4Conventional4-9Steep9+

That is a 4:12 roof (18.43°), a conventional / standard.

  • The pitch 4:12 means the roof rises 4 units for every 12 units of horizontal run.
  • The slope factor of 1.0541 converts flat footprint area to true roof surface: multiply your plan area by it.
  • The rafter (line) length works out to 12.65 in from the wall to the ridge.
  • Most asphalt-shingle roofs sit between 4:12 and 9:12, where standard shingles are rated to shed water.

Next stepMultiply your roof footprint (length × width) by the slope factor to estimate material area.

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