Roof pitch calculator
Roof pitch is the angle of the slope. A roof 7 m wide with a 2.5 m rise at the ridge has a pitch of about 35.5°, and each rafter is 4.30 m from wall to ridge.
- Rise
- 2.50 m
- Rafter length with overhang
- 4.60 m
- Wall to ridge along slope
- 4.30 m
- Roof area, both slopes
- 82.8 m²
A 7 m wide pitched roof with a 2.5 m rise at the ridge, plus 0.3 m overhang at the eaves.
For a simple pitched roof with two equal slopes. Rafter lengths don’t include cuts at the ridge or birdsmouth; check with your timber merchant or roofer.
Rise for common pitches
Rise and slope length for every metre of run (half the span).
| Pitch | Rise per metre of run | Slope per metre of run |
|---|---|---|
| 15° | 0.27 m | 1.04 m |
| 22.5° | 0.41 m | 1.08 m |
| 30° | 0.58 m | 1.15 m |
| 35° | 0.70 m | 1.22 m |
| 40° | 0.84 m | 1.31 m |
| 45° | 1.00 m | 1.41 m |
| 50° | 1.19 m | 1.56 m |
How we calculate this
For a roof with two equal slopes, each side covers half the span. That half-span (the run), the rise and the slope form a right-angled triangle, so the pitch comes from trigonometry and the slope length from Pythagoras.
The roof area is the rafter length (including overhang) times the length of the roof, for both slopes.
Questions people ask
How do I measure the pitch of my roof?
From inside the loft, measure from the top of the wall plate up to the underside of the ridge for the rise, and half the width of the house for the run. You can also hold a spirit level and angle finder against a rafter.
What pitch do roof tiles need?
Each tile has a minimum pitch set by its maker, and it varies a lot between tile types. Check the manufacturer’s guidance for the tile you want before you design the roof.
What is a 45 degree roof as a ratio?
The rise equals the run: 1 m up for every 1 m across. A 30° roof rises about 0.58 m for every metre.
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