Roof Tile Calculator — How Many Tiles Do I Need?

Our roof tile calculator works by multiplying your total roof area by the coverage rate for your selected tile type, then adding an appropriate wastage allowance. Coverage rates are based on standard UK tile sizes and manufacturers' installation guidelines.

The formula

Tiles needed = Roof area (m²) × Tiles per m² × (1 + Wastage %)

If entering dimensions, roof area is calculated as: Length × Rafter length × 2 (for both sides of a standard gable roof).

Coverage rates used

• Concrete Interlocking: ~10 tiles/m² at a 100mm headlap (e.g. Marley Mendip and Marley Ludlow Major 420×330mm, BMI Redland Renown 418×330mm — all 9.7–10.5/m² depending on headlap)
• Plain Clay: ~60 tiles/m² (double-lap, 265×165mm at 100mm gauge — e.g. traditional handmade or machine-made)
• Natural/Artificial Slate: ~20 tiles/m² for the common 500×250mm slate at a 100mm lap, where gauge = (length − lap) ÷ 2 = 200mm. Other slate sizes differ (600×300mm ≈ 13/m², 400×250mm ≈ 27/m²) — use the custom rate for those.
• Large Format Concrete: ~8 tiles/m² for genuinely oversized tiles (e.g. Forticrete SL8, marketed as “just 8 tiles per m²”). Note that “large format” tiles such as Marley Edgemere and Redland Renown still cover at ~10/m², so use the Concrete Interlocking option for those.

Wastage allowances

Standard wastage is 10% for most tiles to cover cutting at verges, hips and valleys. Plain clay tiles have a higher 15% default because the smaller tile size means more cuts. For complex roof shapes, you may want to increase the wastage further.