Roof pitch calculator
Work out a roof's pitch in degrees, and the length of its rafters.
Uses only the sizes you enter.
Result
The roof pitch is 32°, with rafters 4.717 m long.
degrees
| Rafter length | 4.717 m |
|---|---|
| Rise in every 12 of run | 7.5 in 12 |
| As a percentage | 62.5% |
Show the workings
| Step | Sum | Answer |
|---|---|---|
| Run, half the span | 8 m ÷ 2 | 4 m |
| Pitch | tan⁻¹(2.5 m rise ÷ 4 m run) | 32.005 ° |
| Rafter, wall plate to ridge | √(2.5² + 4²) | 4.717 m |
What this leaves out or assumes
- Measured to the line of the rafter, before any birdsmouth or ridge board is cut.
Where the figures come from
This sum uses only the numbers you entered.
How to work out roof pitch
The pitch is the angle whose tangent is the rise divided by the run. The run is half the span for a roof with two equal slopes. A roof 8 m wide and 2.5 m high has a run of 4 m, so its pitch is tan⁻¹(2.5 ÷ 4) = 32°.
The rafter length, from the wall to the ridge, is the hypotenuse: √(rise² + run²). Add the overhang if the rafters stick out past the wall.
The lowest pitch a roof covering can be laid at is set by its maker: check the tile or sheet maker's guide before you choose a pitch.