Buying the right number of tiles avoids both a mid-project shortage and excess leftover stock. This calculator works out how many tiles you need from your room dimensions, the tile size, and a waste allowance for cuts and breakage.
The formula
room area = room length × room width
tile area = (tile size ÷ 100)²
tiles needed = (room area ÷ tile area) × (1 + waste % ÷ 100)
For a 4 m by 3 m room (12 m²) using 30 cm × 30 cm tiles (0.09 m² each) with a 10% waste allowance: 12 ÷ 0.09 = 133.3 tiles, × 1.10 = about 147 tiles.
Choosing a waste allowance
| Layout | Typical waste allowance |
|---|---|
| Simple rectangular room, straight layout | 5–10% |
| Room with alcoves, obstacles, or fixtures | 10–15% |
| Diagonal layout or intricate pattern | 15–20% |
Step-by-step guide
- Measure the room's length and width.
- Measure your chosen tile's side length (assumes square tiles).
- Calculate room area and tile area, then divide to get the base tile count.
- Add a waste allowance based on your layout complexity.
- Round up to the nearest full box, since tiles are sold in fixed box quantities.
Common mistakes
- Forgetting grout lines. This calculator doesn't account for grout spacing, which slightly reduces the effective coverage per tile — a small waste buffer helps absorb this.
- Not rounding up to full boxes. Tiles are sold by the box, not individually — always round your final number up.
- Skipping the waste allowance. Cuts around edges and corners waste partial tiles that can't always be reused.
Frequently asked questions
How many tiles do I need for a room?
Divide the room's area by a single tile's area, then add a waste allowance (typically 10%) for cuts and breakage.
Does this calculator account for grout lines?
Not directly — grout spacing slightly reduces effective coverage. Include a waste buffer to help absorb this along with cut tiles.
Should I round up when buying tiles?
Yes — tiles are sold in fixed box quantities, so round your final calculated number up to the nearest full box.