Roof Pitch Calculator
Last updated: 12 August 2026
Enter the rise and run of your roof to get the pitch in degrees, the rise:run ratio, and the rafter length (excluding overhang). Works in any unit as long as you use the same one for both.
How the calculation works
Pitch angle = arctangent(rise ÷ run). The rafter length comes from Pythagoras: √(rise² + run²). Add your eaves overhang to the rafter figure when ordering timber.
The slope factor converts flat plan area into actual roof area: multiply the footprint by the slope factor to get the true surface area for tiles, felt and battens.
Roof pitch conversion chart
| Degrees | Rise per metre | Ratio | Notes |
|---|---|---|---|
| 10° | 176 mm | 1 : 5.67 | Low pitch — limited tile options |
| 14° | 250 mm | 1 : 4 | "1 in 4" pitch |
| 15° | 268 mm | 1 : 3.73 | Minimum for many interlocking tiles |
| 22.5° | 414 mm | 1 : 2.41 | Common low-pitch tile limit |
| 30° | 577 mm | 1 : 1.73 | Typical UK house roof |
| 35° | 700 mm | 1 : 1.43 | Minimum for many plain tiles |
| 40° | 839 mm | 1 : 1.19 | Steeper modern housing |
| 45° | 1000 mm | 1 : 1 | Steep / period style |
Frequently asked questions
What is the minimum roof pitch for tiles in the UK?
It depends on the tile: many concrete interlocking tiles work down to 15 to 22.5 degrees, plain tiles typically need 35 degrees or more, and natural slate usually needs at least 20 to 25 degrees. Always check the manufacturer minimum pitch for the specific product.
What is a 1-in-4 roof pitch in degrees?
A 1-in-4 pitch, which is 250mm of rise per metre of run, is approximately 14 degrees.
How do I measure the rise and run of a roof?
The run is the horizontal distance from the wall plate to a point under the ridge, often half the building span for a symmetrical roof. The rise is the vertical height from that level to the ridge. Measure both in the same units.
What roof pitch is 30 degrees as a ratio?
A 30-degree pitch is roughly a 1:1.73 rise-to-run ratio, or about 577mm of rise per metre of run.
What pitch is a typical UK house roof?
Most UK house roofs are pitched between 30 and 40 degrees. Modern estate houses often sit around 35 degrees, while period properties can be steeper.
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Estimates are for guidance only. Material dimensions, densities and coverage vary by supplier — always confirm quantities before ordering, and consult a qualified professional for structural work.