Offcut WorksRoof tiles calculator
Enter the roof size and pitch, then the batten gauge and cover width from your tile maker's data sheet. You get the roof area, the rows of battens and the number of tiles.
How the numbers are worked out
Rafter length = run ÷ cos(pitch). A 3 m run at 30° is 3 ÷ 0.866 = 3.46 m. Add the overhang to get the length of the slope to tile.
Rows of battens = slope length ÷ gauge, rounded up. Tiles per row = roof length ÷ cover width, rounded up. Tiles = rows × tiles per row × slopes, plus the spare.
As a cross-check, tiles per m² = 1,000,000 ÷ (gauge × cover width), and that times the roof area gives a similar number.
Get the gauge and cover width from the maker
Every tile has its own batten gauge and cover width, and the gauge depends on the roof pitch and the minimum lap. The example values (100 mm gauge and 165 mm cover) are for a plain clay tile of 265 × 165 mm, and are not a recommendation. Take the figures from the data sheet for the tile you are buying, and note the minimum pitch for it.
What is not included
- Hips, valleys, dormers and chimneys, which need extra tiles and cutting.
- Verge tiles, eaves courses and half tiles. Many makers sell these separately.
- Underlay, membrane, fixings, vents and lead flashing.
Complicated roofs are best priced by a merchant from your drawing. Use this calculator for simple roofs and for a sense check.
Roof area
The area counted is slope length × roof length × the number of slopes. It does not deduct openings such as roof windows. Add the extra for hips and valleys separately.
Questions
How many roof tiles do I need per square metre?
It depends on the tile. Divide 1,000,000 by the gauge and the cover width in millimetres. A plain tile with a 100 mm gauge and 165 mm cover is about 61 per m². The data sheet gives the figure for your tile.
What is the batten gauge?
The distance between the battens, measured along the slope. It sets how much of each tile is exposed. The tile maker specifies it.
Does this include the ridge?
It gives the ridge length, and the number of ridge tiles if you enter their cover. Hips and valleys are not included.
Where the defaults come from
Show the 1 source
- Geometry. The rafter length, rows and counts are geometry. The calculator does not hold any tile maker's data, so you enter the gauge and cover width from the data sheet.
- The gauge and cover width are examples for a plain clay tile. They are not figures from a data sheet, and we did not find a source to set them for every tile.
- We did not give minimum pitch or lap, because they depend on the tile and the maker.
- The 10% spare is our own allowance.