UK and European roof pitch is quoted in degrees, not X/12. Enter rise and run in millimetres to get the pitch in degrees, the slope factor, and the US X/12 equivalent for cross-referencing American specification sheets.
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| Pitch | Angle | Slope % | Multiplier | Hip / valley | Rafter per 12" run |
|---|---|---|---|---|---|
| 0.25/12 | 1.19° | 2.08% | 1.0002 | 1.4144 | 12.00" |
| 0.5/12 | 2.39° | 4.17% | 1.0009 | 1.4148 | 12.01" |
| 1/12 | 4.76° | 8.33% | 1.0035 | 1.4167 | 12.04" |
| 1.5/12 | 7.13° | 12.50% | 1.0078 | 1.4197 | 12.09" |
| 2/12 | 9.46° | 16.67% | 1.0138 | 1.4240 | 12.17" |
| 2.5/12 | 11.77° | 20.83% | 1.0215 | 1.4295 | 12.26" |
| 3/12 | 14.04° | 25.00% | 1.0308 | 1.4361 | 12.37" |
| 3.5/12 | 16.26° | 29.17% | 1.0417 | 1.4440 | 12.50" |
| 4/12 | 18.43° | 33.33% | 1.0541 | 1.4530 | 12.65" |
| 4.5/12 | 20.56° | 37.50% | 1.0680 | 1.4631 | 12.82" |
| 5/12 | 22.62° | 41.67% | 1.0833 | 1.4743 | 13.00" |
| 5.5/12 | 24.62° | 45.83% | 1.1000 | 1.4866 | 13.20" |
| 6/12 | 26.57° | 50.00% | 1.1180 | 1.5000 | 13.42" |
| 6.5/12 | 28.44° | 54.17% | 1.1373 | 1.5144 | 13.65" |
| 7/12 | 30.26° | 58.33% | 1.1577 | 1.5298 | 13.89" |
| 7.5/12 | 32.01° | 62.50% | 1.1792 | 1.5462 | 14.15" |
| 8/12 | 33.69° | 66.67% | 1.2019 | 1.5635 | 14.42" |
| 8.5/12 | 35.31° | 70.83% | 1.2255 | 1.5817 | 14.71" |
| 9/12 | 36.87° | 75.00% | 1.2500 | 1.6008 | 15.00" |
| 9.5/12 | 38.37° | 79.17% | 1.2754 | 1.6207 | 15.31" |
| 10/12 | 39.81° | 83.33% | 1.3017 | 1.6415 | 15.62" |
| 11/12 | 42.51° | 91.67% | 1.3566 | 1.6853 | 16.28" |
| 12/12 | 45.00° | 100.00% | 1.4142 | 1.7321 | 16.97" |
| 13/12 | 47.29° | 108.33% | 1.4743 | 1.7815 | 17.69" |
| 14/12 | 49.40° | 116.67% | 1.5366 | 1.8333 | 18.44" |
| 15/12 | 51.34° | 125.00% | 1.6008 | 1.8875 | 19.21" |
| 16/12 | 53.13° | 133.33% | 1.6667 | 1.9437 | 20.00" |
| 18/12 | 56.31° | 150.00% | 1.8028 | 2.0616 | 21.63" |
| 20/12 | 59.04° | 166.67% | 1.9437 | 2.1858 | 23.32" |
| 24/12 | 63.43° | 200.00% | 2.2361 | 2.4495 | 26.83" |
| Roof covering | Minimum pitch | US equivalent | Standard |
|---|---|---|---|
| Plain clay tiles | 35° | 8.40/12 | BS 5534 |
| Concrete interlocking tiles | 17.5° | 3.78/12 | BS 5534 |
| Large format interlocking tiles | 15° | 3.22/12 | BS 5534 |
| Natural slate | 20° | 4.37/12 | BS 5534 |
| Fibre cement slate | 20° | 4.37/12 | BS 5534 |
| Standing seam metal | 5° | 1.05/12 | Manufacturer |
| Single-ply membrane | 1° | 0.21/12 | BS 6229 |
What is the standard roof pitch in the UK?
Most UK houses sit between 30 and 45 degrees. New builds are commonly 35 to 40 degrees. Victorian and Edwardian properties are often steeper, at 40 to 50 degrees.
How do I convert an American 6/12 spec to degrees?
A 6/12 pitch is 26.57 degrees. The formula is arctan(rise ÷ 12). This comes up constantly when reading US product literature against a British roof.
How do I measure pitch with a spirit level?
Hold a one metre level horizontally against the underside of a rafter, then measure the vertical drop from the far end of the level down to the rafter. Divide the drop in millimetres by 1000 and take the arctangent.
