Why most tile calculators give you the wrong number
Ask a typical online calculator how many 60 × 60 tiles cover 120 m² and it divides 120 by 0.36 and tells you 334. That is wrong in two directions at once, and the errors do not cancel.
First, it ignores the joint. A 60 × 60 tile with a 3 mm grout line occupies 60.3 × 60.3 cm on the floor, which is 0.3636 m², not 0.36. Over 120 m² that difference is four tiles. Second — and much more importantly — it stops at the tiles. You cannot lay a floor with tiles alone. That job also needs roughly 23 bags of adhesive and 4 bags of grout, and if you arrive on site without them the tiles are useless.
The full answer for 120 m², 60×60 tiles, 8% waste
- 357 tiles — 330 to cover the floor, 27 for cuts and breakage
- 129.6 m² of tile purchased for a 120 m² floor
- 23 bags of adhesive (25 kg) at a 10 mm notched trowel
- 4 bags of grout (5 kg) — 19.2 kg at 0.16 kg per m²
- 1,428 spacers
How the consumables are worked out
Adhesive follows the trowel, and the trowel follows the tile
Adhesive is not a fixed rate per square metre. It depends on the notched trowel you use, and the trowel depends on tile size — a bigger tile needs a deeper bed to bridge substrate variation. Typical figures are 2.6 kg/m² at a 6 mm notch, 3.4 at 8 mm, 4.3 at 10 mm and 5.1 at 12 mm. Above 60 cm the tile should also be back-buttered, which adds roughly half as much again. That is why a large-format floor can use nearly three times the adhesive of a small-tile floor over the same area.
Grout follows the joint length, not the area
The standard formula is:
kg/m² = ((L + W) ÷ (L × W)) × thickness × joint width × density
with tile dimensions in millimetres and grout density around 1.6. For 600 × 600 tiles, 10 mm thick, with 3 mm joints, that gives 0.16 kg/m². Now try 100 × 100 mosaic at the same joint width: 0.77 kg/m² — nearly five times more, because small tiles pack far more joint length into each square metre. This is the calculation people most often guess at, and guessing is why grout either runs out mid-job or sits unopened for years.
Choosing a waste percentage
| Situation | Typical allowance |
|---|---|
| Straight layout, simple rectangular room | 10% |
| Small room with many cuts | 12–15% |
| Diagonal layout | 15% |
| Herringbone or complex pattern | 15–20% |
| Large format tiles (offcuts rarely reusable) | 12–15% |
Whatever figure you use, buy the spare tiles in the same batch. Tile shade varies between production runs, and a repair two years later with a different batch is visible from across the room.
What these numbers are and are not
The consumption rates here are typical industry figures, not manufacturer data. Real coverage varies with substrate flatness, trowel technique, ambient temperature and the specific product. Always check the datasheet on the bag you actually buy, and treat these results as a purchasing plan to verify rather than a guarantee. Costs are whatever prices you enter — there is no price database behind this site.