Underordering tiles is a costly mistake — a few tiles short means waiting weeks for restock, hoping the batch still matches, or living with a visible difference in your finished floor. This guide gives you the exact calculation method, including the pattern waste factors that most people miss.
The Basic Tile Formula
Tiles needed = Area (m²) ÷ Individual tile area (m²)
Individual tile area = (Tile width + Grout gap) × (Tile height + Grout gap)
Add waste factor: 10% straight lay, 15% diagonal, 20%+ for complex patterns
Worked Example: 600×600mm Floor Tiles, 6m × 4m Room
- Room area: 6 × 4 = 24 m²
- Tile area (with 3mm grout): (0.600 + 0.003) × (0.600 + 0.003) = 0.603 × 0.603 = 0.3636 m²
- Tiles needed (straight): 24 ÷ 0.3636 = 66 tiles
- Add 10% waste: 66 × 1.10 = 72.6 → buy 75 tiles
Tile Size and Grout Gap Guide
| Tile size | Recommended grout gap | Tiles per m² |
|---|---|---|
| 100×100mm | 2–3 mm | ~96 tiles |
| 200×200mm | 2–3 mm | ~24 tiles |
| 300×300mm | 3 mm | ~11 tiles |
| 300×600mm | 3 mm | ~5.5 tiles |
| 600×600mm | 3–5 mm | ~2.75 tiles |
| 600×1200mm | 3–5 mm | ~1.38 tiles |
| Mosaic (300mm sheets) | N/A (pre-set) | ~11 sheets |
Waste Factors by Lay Pattern
| Pattern | Waste % | Notes |
|---|---|---|
| Straight (grid) | 10% | Most tiles align to room edges |
| Brick bond (offset) | 10–12% | Half-tile offsets increase end cuts |
| Diagonal (45°) | 15–20% | All edges require angled cuts |
| Herringbone | 20–25% | Complex cutting, many small pieces |
| Chevron | 25–35% | Specialist cut; use a professional |
Calculating Wall Tiles
Wall tiles are calculated the same way as floor tiles, but you deduct door and window openings:
- Measure each wall height and width separately
- Calculate area of each wall
- Subtract doors (approx. 1.8 m²) and windows (approx. 1.2 m²) from the relevant walls
- Add all wall areas together
- Apply tile formula and waste factor
How Many Extra Tiles to Order
Always order at least 10% extra, but consider ordering 15% for the following situations:
- The space has many awkward angles, niches, or irregular walls
- The tiles are large (600mm+) — large tiles have proportionally more cuts at edges
- You're tiling diagonally or in a complex pattern
- The tiles are expensive or hard to source — keep extras for future repairs
- You're a beginner tiler — even experienced tilers break or mis-cut tiles
Always buy from the same batch (check the shade lot number on each box) and store unopened boxes in case of future damage. Replacement tiles from a different batch may not match.