About this calculator
Full pitched-roof takeoff: true roof area, number of tiles or slates, battens at the right gauge, membrane rolls, ridge and hip tiles, and fixings. Works for gable, hip and mono-pitch roofs.
How it’s calculated
True roof area = plan area including overhang × pitch factor, where pitch factor = √(1 + (rise ÷ run)²). Hip roofs with the same pitch on every side have the same area as a gable over the same footprint. Only the edges differ. Hip length = (half width) × √(2 + (rise ÷ run)²).
Tiles per m² depend on the gauge (exposed length) and cover width of the product. The figures used here are typical. Your tile maker’s gauge table takes priority.
Worked example
With these inputs:
- Roof shape
- Gable (two slopes)
- Building length (wall to wall)
- 10 m
- Building width (wall to wall)
- 8 m
- Overhang (eaves and verge)
- 300 mm
- Pitch entered as
- Degrees
- Pitch in degrees
- 35
- Roof covering
- Interlocking concrete tiles
- Waste allowance
- 10%
the result is:
- Tiles / slates needed
- 1,212 tiles
- Roof surface area
- 111.29 m²
- Plan area (with overhang)
- 91.16 m²
- Pitch factor
- × 1.221 (35°, 8.4/12)
- Eaves length
- 21.2 lin m
Tips from the trade
- Valleys, dormers and chimneys add waste. Go to 15–20% on cut-up roofs.
- Check the tile maker’s minimum pitch and headlap for your wind and rain exposure zone.
- Order ridge material for the hips too. It is the most commonly forgotten line.
Common questions
How many bundles of shingles per square?
Three for most architectural and 3-tab shingles. Some heavy designer shingles are 4 or 5.
How many roof tiles per m²?
About 10 for large interlocking concrete tiles, 60 for plain tiles and about 20 for 500 × 250 slates.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the Building Regulations before ordering.