How to use this roof pitch calculator
- Rise, enter the vertical height the roof climbs.
- Run, enter the horizontal distance over which it climbs (this defaults to 12).
- Read your pitch, angle, slope and rafter length, they update instantly as you type.
Use the same unit for both boxes (inches, centimetres or any plain number).
What roof pitch means
Roof pitch describes how steep a roof is, measured as rise over run: the vertical height it gains for a given horizontal distance. Builders almost always express this against a run of 12, which is where the x:12 notation comes from. A 4:12 roof rises 4 for every 12 it travels sideways, while an 8:12 roof is twice as steep. To turn that ratio into an angle in degrees, take the arctangent of rise divided by run and convert from radians, so a 6:12 pitch is roughly 26.6 degrees. The same ratio written as a slope percentage is simply rise divided by run times 100, so a 6:12 pitch is a 50 percent slope. The rafter length is the diagonal of that triangle, found with the Pythagorean theorem, and tells you how long the sloped run is before any overhang is added.
Common roof pitches
- Low slope (2:12 to 4:12): gentle roofs, common on porches, extensions and modern designs.
- Conventional (4:12 to 9:12): the everyday range for most houses, easy to walk and shed water well.
- Steep (9:12 and above): dramatic, fast-draining roofs seen on traditional and snowy-region homes.
Pitch affects which roofing materials you can use, how well the roof drains, and how much surface area you are covering, so it is worth knowing before you order materials or quote a job. Treat the numbers here as a planning guide and confirm measurements on site.
Frequently asked questions
How is roof pitch calculated?
Pitch is the rise (vertical height) divided by the run (horizontal distance), expressed against a run of 12: pitch = (rise ÷ run) × 12. A rise of 6 over a run of 12 gives a 6:12 pitch.
What does a 6:12 roof pitch mean?
It rises 6 units for every 12 units of horizontal run. That is an angle of about 26.6 degrees and a slope of 50 percent.
How do I convert roof pitch to an angle?
Take the arctangent of rise divided by run and convert to degrees: angle = atan(rise ÷ run) × 180 ÷ π. The calculator does this automatically.
What is the rafter length figure?
It is the sloped distance across your rise and run, from the Pythagorean theorem: rafter = √(rise² + run²). It is the diagonal length per unit of run, before any overhang.
How do I convert roof pitch to an angle in degrees?
Take the arctangent of rise divided by run, then convert to degrees: angle = atan(rise ÷ run) × 180 ÷ π. This calculator does it for you the moment you enter the figures.