Most quantity mistakes we see on site come from one thing: counting the tile face and forgetting the joint. A 9×3 inch tile does not cover 27 square inches of wall. With a 10 mm joint it takes up closer to 32, and that gap adds up across a whole wall.
The formula for brick tiles per sq ft
Add the joint width to the length and the height of the tile, multiply, and divide 144 (the square inches in a square foot) by the result. A 10 mm joint is about 0.39 inch.
For a 9×3 tile with a 10 mm joint: (9 + 0.39) × (3 + 0.39) = 31.9 square inches. 144 ÷ 31.9 = 4.52 tiles per sq ft.
Tiles per sq ft for each size we make
| Tile face | No joint | 6 mm joint | 10 mm joint | 12 mm joint |
|---|---|---|---|---|
| 9" × 3" | 5.33 | 4.82 | 4.52 | 4.38 |
| 9" × 2" | 8.00 | 6.97 | 6.40 | 6.15 |
| 9" × 1.5" | 10.67 | 8.98 | 8.09 | 7.71 |
| 6" × 3" | 8.00 | 7.14 | 6.64 | 6.41 |
The "no joint" column is only useful as a ceiling. Nobody lays brick tiles butt-jointed, and a supplier who quotes on that basis is quoting you more tiles than you need.
A worked example
Take a 12 ft wide, 9 ft high living room wall with a 3 × 7 ft door in it. The wall is 108 sq ft, the door is 21 sq ft, so the tiled area is 87 sq ft.
- In 9×3 with a 10 mm joint: 87 × 4.52 = 393 tiles. Add 7% for cuts and you order 421.
- In 9×1.5 with the same joint: 87 × 8.09 = 704 tiles, or 754 with 7% added.
The slim tile needs almost twice as many pieces for the same wall, which also means more labour. Factor that into the installer’s rate, not just the tile price.
How much wastage to allow
Five percent is enough for a plain rectangular wall. Go to eight or ten percent if the wall has several windows, external corners, a herringbone pattern or a lot of cut pieces around switches and pipes. With handmade tiles, keep a few extra so the mason can reject odd pieces while mixing boxes.
You can skip the arithmetic: the quantity calculator on our price page does it for any wall and sends the result to us for a quote.
