Pitch describes how steep a roof is. It changes the roof area, which coverings you can use, how safe the roof is to work on, and how much it costs.
Three ways of saying the same thing
- Rise in 12 (x/12): how many inches the roof rises for every 12 inches of horizontal run. Standard in the US.
- Degrees: the angle from horizontal. Standard in the UK and in tile makers' data.
- Percent: rise ÷ run × 100. Used for low-slope roofs and drainage.
| x/12 | Degrees | Percent |
|---|---|---|
| 2/12 | 9.5° | 16.7% |
| 3/12 | 14.0° | 25% |
| 4/12 | 18.4° | 33.3% |
| 6/12 | 26.6° | 50% |
| 8/12 | 33.7° | 66.7% |
| 9/12 | 36.9° | 75% |
| 12/12 | 45° | 100% |
How to measure an existing roof
- Hold a level horizontally with one end touching the roof surface.
- Measure 1 metre along the level.
- Measure straight down from that mark to the roof. That is the rise.
From inside the loft, a digital angle finder on the underside of a rafter gives degrees directly.
Why it matters for quoting
Steeper roofs mean more area, more material, slower work and often scaffolding or extra safety equipment. Many roofers add a steep-roof charge above about 35°.
This guide is general information for estimating. It is not engineering, legal or tax advice. Check the Building Regulations and Building Control for your project.