Roofing Calculator — Tiles, Shingles, Felt & Battens
Calculate the number of roof tiles or shingle bundles, underlay (felt), roof battens and ridge tiles for gable and hip roofs. Enter plan dimensions and roof pitch to get total roof area and a complete material list.
How the roofing calculator works
- 1Plan area = footprint length × footprint width (m²)
- 2Roof area: plan area ÷ cos(pitch angle) — a 35° pitch multiplies area by 1.22
- 3Tile count: roof area ÷ tile coverage per tile (from manufacturer data)
- 4Apply 10% waste for cuts at hips, valleys, verges and ridge
- 5Batten length: tile rows × roof width; battens at gauge spacing (e.g. 100 mm for plain tiles)
- 6Underlay (felt): roof area + 150 mm overlaps; ridge tiles: ridge length + 10% for cutting
Worked example
Gable roof: 10 m × 8 m plan, 35° pitch, concrete interlocking tiles covering 0.2 m² each.
Roof area: 80 m² ÷ cos(35°) = 97.6 m². With 10% waste: 107 m². You need 540 tiles, 115 m² of underlay and 20 ridge tiles.
Frequently asked questions
How do I calculate roof area from ground measurements?
Measure the building footprint length and width. Multiply by the pitch factor: flat (0°) = 1.0, 25° = 1.10, 35° = 1.22, 45° = 1.41. This gives you the actual sloped roof area.
How many roof tiles do I need per m²?
This varies by tile type: concrete interlocking tiles 8–10 per m², clay plain tiles 60–65 per m², slate 25–30 per m². Always use the manufacturer's coverage figure for the specific product.
What is the minimum roof pitch for tiles?
Concrete interlocking tiles: minimum 15–17.5° depending on exposure. Clay plain tiles: 35° minimum. Profiled clay pantiles: 15°. Below the minimum pitch, moisture can be driven under the tiles in heavy rain.
How many bundles of shingles do I need for 100 m²?
One square = 100 sq ft (9.29 m²). Most three-tab shingles cover one square per 3 bundles, architectural shingles may need 4 bundles per square. For 100 m² (10.76 squares): approximately 32–43 bundles.
Do I need underlay under roof tiles?
Yes — breathable roofing membrane (underlay/felt) is required under all tiled roofs in most building codes. It provides a secondary line of defence against wind-driven rain and condensation management.