How this calculator works
A roof tile overlaps the ones below it, so each row of tiles covers less than the tile's full length. The distance between rows is the batten gauge: for plain tiles laid in a double lap it is half of the length less the headlap, and for interlocking tiles laid in a single lap it is the length less the headlap. Each tile covers a width of roof (its cover width), so the number of tiles per square metre is one divided by the gauge times the cover width. The roof is measured along the slope, which is longer than the plan width by the cosine of the pitch.
Worked example: a gable roof 8 × 6 m at 30° has a slope of 3.64 m, so 58.9 m² of roof in all. Plain tiles of 265 × 165 mm with a 65 mm headlap have a gauge of 100 mm and need 60.6 per m²: 3929 tiles with 10% waste, 589 m of batten, 21 ridge tiles and 2 rolls of underlay. Interlocking tiles of 420 × 330 mm have a gauge of 345 mm and need 9.7 per m², or 627 tiles. A steeper pitch of 40° makes the roof 66.6 m², and a 12 × 8 m house needs 7732 plain tiles.
Tiles for common houses (30°, 8 × 6 m ridge and eaves, 10% waste)
Plain tiles and interlocking concrete tiles for gable roofs.
| Building | Roof area | Plain tiles | Interlocking tiles |
|---|---|---|---|
| 6 × 5 m | 37 m² | 2,489 | 397 |
| 8 × 5 m | 50 m² | 3,305 | 527 |
| 8 × 6 m | 59 m² | 3,929 | 627 |
| 10 × 6 m | 73 m² | 4,899 | 781 |
| 10 × 7 m | 85 m² | 5,676 | 905 |
| 12 × 8 m | 116 m² | 7,732 | 1,233 |
Tips before you buy
- The batten gauge sets how many tiles you need, and the maker's gauge for your pitch must be used: check the data sheet.
- Plain tiles need about 60 per m², and interlocking concrete tiles about 10 per m², so the cost per m² differs a lot, as does the weight.
- The minimum pitch depends on the tile: plain tiles usually need 35° or more, and many interlocking tiles work down to 22.5° or lower.
- Order 5 to 10% extra for cuts at the verges, hips and valleys, and keep a few spare in case of damage.
- Check the roof structure can carry the weight of the tiles, and use breathable underlay and the right fixings for your area, which depend on the wind exposure.
Tools & materials for this project
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Frequently asked questions
How many roof tiles per square metre?
About 61 for plain tiles (265 × 165 mm at a 100 mm gauge) and 10 for interlocking concrete tiles (420 × 330 mm). The gauge and cover width from the tile maker give the exact figure.
How many tiles for an 8 x 6 m roof?
3929 plain tiles, or 627 interlocking tiles, for a gable roof at 30° with 10% waste: 59 m² of roof.
How do you work out the batten gauge?
For a double lap, (tile length − headlap) ÷ 2: 100 mm for a 265 mm tile with a 65 mm headlap. For a single lap, tile length − headlap: 345 mm for a 420 mm tile with a 75 mm headlap.
How much does the pitch change the area?
The roof area is the plan area divided by the cosine of the pitch. At 30° the 8 × 6 m roof is 58.9 m², and at 40° it is 66.6 m².
How many ridge tiles do I need?
About one for every 400 mm of ridge: 21 for an 8.1 m ridge (the 8 m building plus the verges).
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.