Roof Tile Calculator
How many clay or concrete roof tiles you need: barrel (Spanish), Roman, flat or concrete tiles from the roof plan and pitch, with breakage allowance, roof load, battens and cost.
How it works
roof area = plan area ÷ cos(pitch) · tiles = roof area × tiles per m² × (1 + allowance) · load = tiles per m² × weight per tile · battens ≈ roof area ÷ batten gauge
Roof tiles are sold by the piece, and how many cover a square metre depends on the tile and its overlap: clay barrel (Spanish) tiles laid channel-and-cap need about 28 per m², Roman or mixed clay tiles about 12, flat interlocking French tiles about 14 and large concrete interlocking tiles about 10, per manufacturers’ data sheets. Measure the roof on plan including the eaves and the slope factor 1 ÷ cos(pitch) turns it into the real sloped area. Clay and concrete tiles weigh 40–55 kg/m², so check the roof structure, and most makers want at least about 30% (17°) of pitch unless a waterproof underlayment is used. Ridge and hip tiles are counted separately.
Worked example
A 10 × 8 m roof plan (80 m²) at 25° has a slope factor of 1 ÷ cos 25° = 1.103, so the roof surface is 88.3 m². Clay barrel tiles at 28 per m² need 2,472 tiles, or 2,596 tiles with a 5% breakage allowance. They load the roof with about 45 kg/m² (3.95 t in all), need about 294 m of battens at a 30 cm gauge, and cost $2,076.80 at $0.80 each.
Sources: Tile Roofing Industry Alliance — installation manual · Verea / La Escandella clay tile data sheets
Frequently asked questions
How many roof tiles per square metre?
About 28 for clay barrel (Spanish) tiles, 12 for Roman or mixed tiles, 13–15 for flat interlocking tiles and 10 for large concrete tiles. Always check the coverage printed on the maker’s data sheet, as it depends on the overlap and batten gauge.
How do I calculate the roof area for tiles?
Multiply the plan length by the plan width including the eaves overhang, then divide by the cosine of the roof pitch. At 25° the factor is 1.103, so a 80 m² footprint has about 88.3 m² of roof.
How much extra tile should I order?
Add 5% for breakage and cuts on a simple gable roof and 10–15% for hips, valleys and dormers. Keep a few spare tiles for future repairs, as colours change between batches.
How heavy is a tiled roof?
Clay and concrete tiles weigh roughly 40–55 kg per m² (8–11 lb per sq ft), two to four times more than asphalt shingles or metal sheet, so a roof built for light materials may need reinforcing.
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This calculator is for educational purposes. Double-check important results before acting on them.