Tile calculator guide: how many tiles do I need, with cuts and waste

How do I work out how many tiles I need?

The simple method, as set out by FireTile, has three steps:

1. Measure the area. Multiply length by width in metres. Split an L shaped or irregular room into rectangles and add them up, which is what The Tile Association suggests too.
2. Work out one tile’s area. A 297 x 297 mm tile is 0.297 m x 0.297 m, about 0.088 m².
3. Divide, then add waste. FireTile’s example covers 14.5 m²: 14.5 divided by 0.088 is about 165 tiles, plus 10% (17 tiles) gives 182.

Tiles are sold by the box, so round up to the next full box. Tile.co.uk notes that its own box counts are always rounded up so you have enough.

How much extra should I buy?

Different sources give slightly different numbers, but they agree you need some extra:

• Standard tiles: The Tile Association says allow 10% extra for breakages and cutting, and Tile.co.uk says add at least 10%.
• Large format tiles: The Tile Association says larger tiles may need more, and FireTile suggests 20%.
• Diagonal layouts: Tile.co.uk suggests 15% when tiles go at 45 degrees, because every edge needs cuts.
• Spares for repairs: Tile.co.uk suggests keeping 5% spare for future repairs, especially if the range might be discontinued.

The Tile Association also advises buying enough tiles from the same batch and checking the batch number on delivery, so it makes sense to order everything in one go.

Why a tile calculator using area alone can get it wrong

A plain area sum treats tiles like paint: it assumes every scrap gets used. Real tiling does not work like that.

Grout gaps add up. The Tile Association warns against butt jointing tiles; always leave a gap. Those gaps take up space. Eight 300 mm tiles with 3 mm joints between them need 2,421 mm (8 x 300 plus 7 x 3), so they will not fit a 2,400 mm wall. You get 7 full tiles and a cut instead.

Cuts do not always pair up. If the cut piece you need at one edge is wider than half a tile, the offcut from that tile is often too small to use at the other edge. You then use a fresh tile for each cut, and the waste goes up.

The pattern matters. In a half bond (brick style) layout each row is shifted by half a tile, so rows start and end with cut pieces. That usually means more cuts than a straight grid.

This is why a cut list planner, one that lays the tiles out row by row, can give a more useful answer than area alone. It tells you not just how many tiles to buy but what sizes to cut.

How should I plan the tile layout?

The Tile Association’s advice is to carefully set out the tiles before you start. A few practical points:

• Measure each wall or floor area separately and write the sizes down in millimetres.
• Check whether you want to start from the centre or from one wall, as this changes the size of the edge cuts.
• Avoid thin slivers at a visible edge if you can, by shifting the starting point.
• Keep your spare tiles after the job for future repairs.

If you do not want to do the tiling yourself, The Tile Association recommends using one of its member tile fixers.

Questions people ask

Where Tile Layout Planner helps, and where it does not

Tile Layout Planner is our Android app for planning a tiled floor or wall. You enter the room size, the tile size, the grout gap and the tile thickness in millimetres, choose a straight, half bond or third bond layout, and add tiles per box and a waste allowance if you like. You can start from one corner or let the app balance the layout so the cuts on opposite walls are as big and even as they can be, and it warns you about very thin cuts. It works out full tiles, cut sizes, boxes to buy, cut waste in m², and grout and adhesive amounts, with a preview of the layout. It can also reuse offcuts, planning two cut pieces from one tile when they fit, so you buy fewer tiles. Your first 3 layouts show everything with every option. After that the free view still gives tile and box counts, and a one-time unlock brings back every option, the full cut list, preview, grout and adhesive and sharing for unlimited layouts. There is no account and your data stays on your phone.

What it is good for: checking how many boxes to buy and what cuts you will make in a single rectangular room before you go to the shop.

What it will not do: it works for single rectangular rooms. For L shaped rooms you would need to plan each rectangle separately, and it does not handle diagonal or herringbone patterns. Grout and adhesive amounts are estimates, so check the coverage on your bags. It also cannot see your walls, so if they are out of square or uneven, measure carefully and ask a tiler.

Questions or bugs: Email us.

Sources

1. Tile It RightThe Tile Association · tiles.org.uk
2. Calculating Tiles For Your ProjectFireTile · firetile.co.uk
3. Tile CalculatorTile.co.uk · tile.co.uk