Roof pitch calculator
Work out a roof's pitch in degrees (and as a ratio) from its rise and run — useful for tile/slate selection, which often specifies a minimum pitch.
Result
Roof pitch
Pitch ratio
How to use this calculator
- Measure the vertical rise from wall plate to ridge, and the horizontal run (half the roof's span).
- Enter both measurements in metres.
- Read the pitch in degrees and as a ratio.
Assumptions
- Assumes a simple symmetrical gable roof; complex or asymmetric roofs need each slope measured separately.
Technical details: what the fields mean
- Rise
riseM - Vertical height gained from the wall plate to the ridge, in metres.
- Run
runM - Horizontal distance from the wall plate to directly under the ridge (half the total span), in metres.
Methodology
Pitch (degrees) = arctan(rise ÷ run). Pitch ratio expressed as 1:run/rise.
Worked example
2m rise over a 4m run
Inputs: riseM=2, runM=4
Result: 26.6° (approx. 1:2 ratio)
Practical guidance
- Most concrete/clay tiles need a minimum pitch (often 15–22.5° depending on the product) — check your chosen tile's manufacturer data sheet.
- Slate roofs can often go lower than tile roofs — again, check the specific product's minimum pitch.
Common mistakes
- Measuring run as the full roof span instead of half of it.
- Mixing metric and imperial measurements in the same calculation.
FAQs
What roof pitch is 2m rise over 4m run?
About 26.6 degrees, roughly a 1:2 pitch ratio.
What's the minimum pitch for roof tiles?
It depends entirely on the tile product — always check the manufacturer's minimum-pitch specification rather than assuming a generic figure.