What is it?
The Roof Pitch Calculator works out how steep a roof is. It shows the angle, the pitch as x/12, the rafter length, the slope factor and the roof area.
Who is it for?
Builders, carpenters, shed and farmhouse builders, and anyone ordering roofing sheets or tiles.
How to use it
- Enter the Rise (height): from the top of the wall to the ridge.
- Enter the Run (half the width): from the wall to the point below the ridge.
- Optionally, enter the Floor area under the roof (optional) to get the sloped roof area.
Reading pitch
- “6/12” means the roof rises 6 units for every 12 units across, about 26.6°.
- Rafter length here is from wall to ridge; add the overhang (eaves) yourself.
- Slope factor × flat area = sloped roof area. Use it to order sheets or tiles, plus overlap and wastage.
Typical pitches
Metal and cement sheet roofs often use low pitches (around 10–15°); clay tiles usually need 30° or more to shed rain. Check the minimum pitch for your roofing material.
These are estimates for planning and buying. For structural work, follow your engineer’s or contractor’s quantities.
Worked example
Rise 1.5 m over a run of 4 m: pitch ≈ 20.6°, about 4.5/12; rafter ≈ 4.27 m before overhang.
Errors and how to fix them
- “Enter the run (more than 0)”: run is half the building’s width.
Open the tool: Roof Pitch Calculator
Still stuck?
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Questions, or an error not listed here?
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