How the tile calculator works
Tiles are counted, not measured, so the job is to find how many tile "cells" fit into the surface. Each cell is one tile plus half a grout joint on every side, which in practice means the tile length and width each grow by one joint width. That is why a wider joint slightly reduces the number of tiles you need.
Tiles = area ÷ ((tile length + joint) × (tile width + joint)) × (1 + cutting allowance), rounded upThe result is then divided by the number of tiles in a box and rounded up again, because shops rarely split boxes. The allowance depends on the pattern: straight and half-offset layouts lose about 10% in edge cuts and breakage, a 45° diagonal loses around 15% because every perimeter tile is cut on the angle, and herringbone or rooms full of pipes and corners can reach 20%.
Worked example
A kitchen floor of 4 m × 3 m is 12 m². With 60 × 30 cm porcelain tiles and a 3 mm joint, each cell measures 0.603 × 0.303 m = 0.1827 m², so the bare count is 12 ÷ 0.1827 = 65.7 tiles. Adding 10% for a straight layout gives 72.2, rounded up to 73 tiles. At 8 tiles per box (1.44 m²) that is 9.1 boxes, so you buy 10 boxes and keep the spare tiles. Laid on the diagonal the same floor needs 65.7 × 1.15 = 75.5, so 76 tiles, which still fits in 10 boxes.
Common tile sizes and how many fit per square metre
| Tile size | Tiles per m² (no joint) | Imperial equivalent | Typical box |
|---|---|---|---|
| 10 × 10 cm | 100 | 4 × 4 in: 9 per ft² | about 1 m² or 11 ft² |
| 20 × 20 cm | 25 | 8 × 8 in: 2.25 per ft² | 1 m², 25 tiles |
| 30 × 30 cm | 11.1 | 12 × 12 in: 1 per ft² | 11 tiles, about 1 m² or 11 ft² |
| 30 × 60 cm | 5.56 | 12 × 24 in: 0.5 per ft² | 8 tiles, 1.44 m² or 16 ft² |
| 60 × 60 cm | 2.78 | 24 × 24 in: 0.25 per ft² | 4 tiles, 1.44 m² or 16 ft² |
| 60 × 120 cm | 1.39 | 24 × 48 in: 0.125 per ft² | 2 tiles, 1.44 m² or 16 ft² |
Box contents vary between factories, so always read the label: it states both the tile count and the area covered, and the two should agree with the size printed on the tile.
Tips before you order
- Split L-shaped rooms. Measure each rectangle separately, add the areas, then run the total through the calculator once so the allowance is applied only once.
- Check the batch and shade code. Porcelain and ceramic are fired in lots that differ slightly in colour and calibre. Order everything from one lot, and open three or four boxes at a time to blend them.
- Large formats cut badly. A 60 × 120 cm tile that loses a corner cannot be reused elsewhere, so small rooms tiled in big formats often need the 20% setting even in a straight pattern.
- Keep a spare box. Discontinued ranges are common. A cracked tile five years later is easy to replace if a few matching pieces are stored in the garage.
- Walls are measured the same way. Multiply the height by the width of each wall, subtract windows and the bath panel, and enter the result as length × 1.
Frequently asked questions
How many tiles do I need for 100 square feet?
With 12 × 12 in tiles you need 100 tiles plus 10% waste, so about 110. With 12 × 24 in tiles it is 50 plus 10%, so 55 tiles, or 7 boxes of 8.
How much extra tile should I buy for waste?
Add 10% for a straight or brick-offset layout, 15% for a diagonal layout and up to 20% for herringbone, large formats in small rooms or rooms with many obstacles.
How many 60x60 tiles are in a square metre?
Exactly 2.78 without joints. A 25 m² room therefore needs about 70 tiles, or 77 once a 10% allowance is added.
Does the grout joint change the number of tiles?
Yes, slightly. A 3 mm joint with 30 × 60 cm tiles makes each tile cover 1.5% more area, so you need about 1.5% fewer tiles than a joint-free calculation suggests.
Should I count tiles or square metres when I buy?
Buy by the box: calculate the tile count, divide by the tiles per box and round up. Shops sell tile by the square metre or square foot, but only in whole boxes.
Last reviewed: 2026-09-27 · How we calculate