How this calculator works
A row of tiles is made of tiles and grout joints, so a row of w whole tiles is w tiles plus w − 1 joints long. The calculator finds the most whole tiles that fit, measures what is left over and splits it between the two ends, taking off two extra joints (the ones beside the cut tiles).
Worked example: a 3 m by 2.4 m floor in 300 mm tiles with 3 mm joints holds 9 whole tiles along the length with a 135 mm cut at each end, and 7 whole tiles across the width with 138 mm cuts. That is 11 by 9 tiles, so 109 to buy with 10% extra, and 80 cross spacers. In 600 mm tiles the same floor needs 33.
When the cut would be too thin, the calculator drops one whole tile: a floor 2.74 m long would give a centred cut of 5 mm with 9 whole tiles, but with a 50 mm minimum it uses 8 whole tiles and a 157 mm cut.
Assumptions and sources
- Assumptions used: tiles laid straight with a 3 mm joint; the layout is centred in both directions; every cut tile counts as a whole tile to buy (the offcut is not reused); 10% waste added.
- A centred layout puts a cut tile of the same size at each end of every row. Many tilers start from the middle of the room, or from the doorway or the most visible wall, and dry-lay a row to check the cuts before the adhesive goes on. Walls are rarely square, so the cut at one end of a row may differ from the other. This counts the field of tiles: allow for the trim or the skirting that covers the gap at the walls.
The formula and a worked example are shown above, so you can check any result by hand. Read how we calculate and check our numbers. Results are estimates for planning: supplier products vary, so check the size printed on the label.
Whole tiles and edge cuts for a 3 × 2.4 m floor
3 mm joint, layout centred, smallest cut 50 mm.
| Tile size | Whole tiles per row | Edge cut (length) | Tiles to buy |
|---|---|---|---|
| 200 × 200 mm | 14 | 78 mm | 229 |
| 300 × 300 mm | 9 | 135 mm | 109 |
| 400 × 400 mm | 7 | 88 mm | 70 |
| 450 × 450 mm | 6 | 140 mm | 62 |
| 600 × 600 mm | 4 | 293 mm | 33 |
Tips before you buy
- Dry-lay a row of tiles with spacers from wall to wall before you spread any adhesive. It takes ten minutes and shows what the edge cuts will be.
- Aim for edge cuts of at least half a tile. If the calculator gives a thin cut, shift the starting line or change the tile size.
- Start from the most visible line, such as the doorway or a long wall, and let the thin cuts fall where nobody looks.
- Take the spacers out before the grout goes in. Do not leave them in the joint.
- Use spacers the same width as the grout joint. 2 mm and 3 mm are common for wall tiles, and 3 mm to 5 mm for floors.
Tools & materials for this project
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Frequently asked questions
How many tiles fit across a room?
Divide the length plus one joint by the tile plus one joint and round down. A 3 m room in 300 mm tiles with 3 mm joints fits 9 whole tiles.
How big will the cut tiles at the edges be?
Leave out the whole tiles and the joints and divide what is left by two. In the default 3 m room the cut at each end is 135 mm.
How many tile spacers do I need?
One cross spacer goes at each place where four tiles meet, which is the number of tiles in a row less one, times the number of rows less one: 80 for the default floor. They are cheap and small, so buy extra.
Should I start tiling from the centre of the room?
Many tilers do, because it gives equal cuts at both walls. Others start at the doorway or the long wall that is seen most. Either way, dry-lay a row first.
Do I count the cut tiles as whole tiles?
This calculator does, because offcuts rarely fit anywhere else. If you can reuse the cut-off end of one tile at the other end of the row, you may need less.
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Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.