How tile count is calculated
Dividing the area to cover by the area of one tile gives the theoretical tile count. Adding a cutting-waste allowance and rounding up gives the number you should actually buy.
- width × length — area to cover (m²)
- tile width × tile height — area of one tile, converted to m²
- waste% — cutting/breakage allowance (5–15%)
- ⌈ ⌉ — round up to the next whole tile
More detail
How much waste allowance to pick
A straight, butt-jointed lay is normally ordered with a 10% overage as the minimum, dropping to 5% only for very simple cuts. Diagonal or pattern lays such as herringbone leave more offcuts and are usually ordered at 15% or more.
Enter tile size in centimeters
Use the size printed on the tile box (e.g. 300×300, 600×600). Grout joint width isn't included in this calculation, so if your joints are wide, step up to the next waste tier for a safer margin.
Practical tip. Tiles are usually sold by the box, not individually. Divide the calculated count by tiles per box and round up to know how many boxes to order.
Frequently asked questions
How many tiles do I need for a 4m×5m room with 30cm×30cm tiles?
The 20 m² area divided by a 0.09 m² tile gives about 222.2 tiles; adding the 10% waste allowance and rounding up gives 245 tiles — that's exactly the default example above, so just swap in your own numbers.
Which waste percentage should I choose?
For a straight, butt-jointed lay, 10% is the usual minimum overage, and 5% only makes sense when the cuts are very simple. A diagonal or pattern lay like herringbone is usually ordered at 15% or more. More cutting angles mean more offcuts and a higher waste rate.
Why does the tile count get rounded up (⌈ ⌉)?
Tiles can't be bought as fractions, so any decimal result is always rounded up to avoid coming up short. The "Tiles needed" figure above already has this rounding applied — it's the final purchase quantity.
Does this include grout joint width?
No, this calculation only divides area by tile size and doesn't account for grout joints. If your joints are wide or your tiles are small (meaning more joints overall), step up one waste tier (e.g. 5% → 10%) for a safer margin.