How many tiles do I need?

1. The formula, in plain English

Estimating tile is an area problem. You are covering a flat surface — a floor or a wall — with flat pieces, so all that matters is how much surface there is and how much surface one tile provides. The surface area of a rectangle is simply its length times its width. Divide that area by the area of a single tile and you have the number of tiles, before any allowance for the pieces you will cut and discard.

The one twist that makes tile different from, say, paint is waste. Tiles are rigid and come in fixed sizes, so wherever the field meets a wall, a corner, a doorway or a fixture, a tile has to be cut — and the offcut is usually the wrong shape to use anywhere else. That is why every tile estimate adds a waste percentage on top of the bare area before dividing. The whole method is area × (1 + waste) ÷ tile area, rounded up, and that is exactly what the tile calculator does, including the unit conversion if you measured in metres rather than feet.

2. Measuring the area step by step

Start with two numbers: the length and the width of the surface. For a floor, that is the room dimensions; for a wall, it is the wall's width and its height. Take the worked example of a square room 10 ft on each side. The floor area is 10 × 10 = 100 ft². Add a 10% waste allowance and you are buying 110 ft² of tile. With 12 × 12 in tiles, each of which covers exactly 1 ft², that is 110 tiles. Switch to larger 12 × 24 in tiles (2 ft² each) and the same floor needs about 55 tiles; with 24 × 24 in tiles (4 ft² each) it is about 28.

The arithmetic is identical in metric. A 3 × 3 m floor is 9 m². Add 10% to get 9.9 m², and at 0.09 m² per 300 × 300 mm tile that is the same 110 tiles. If a room is L-shaped or has a bay, split it into rectangles, work out each one, and add them together. For walls with a large opening such as a window or a doorway, measure the whole wall and then, only if the opening is genuinely large, subtract its area — small openings are best left in, because the offcuts around them rarely save you a tile and the extra becomes part of your safety margin.

3. Tile sizes and coverage

Tile size is the biggest lever on your count. Small mosaic and subway tiles mean many more pieces and far more grout joints; large-format tiles cover ground quickly with fewer joints but are heavier to handle and less forgiving on an uneven surface. Here is the coverage of common sizes, with how many it takes to cover 100 ft² before waste:

The “per 100 ft²” column is before waste — add your allowance on top. Note how the piece count drops sharply as tiles get bigger: a floor that needs 100 of the 12 × 12 in tiles needs only 25 of the 24 × 24 in size. Fewer pieces means less grout to mix and far less time on your knees, but it also means each cut wastes a bigger tile, so large-format jobs often warrant a slightly higher waste percentage even on a straight lay.

4. Waste, layout patterns and how much to actually buy

Waste is where tile estimates live or die. The standard allowance for a simple straight (grid) layout is about 10%, which covers the perimeter cuts, the trims around fixtures and the occasional cracked tile. The moment you rotate the grid, the figure climbs: a diagonal layout creates triangular offcuts at every edge, so plan on roughly 15%. A herringbone, basketweave or modular multi-size pattern wastes the most — up to about 20% — because the cuts are frequent and oddly shaped. If you are new to tiling, lean toward the higher end of these ranges; a spare box is cheap insurance against a stalled job.

A second reason to round up generously is the layout itself. Centring the pattern in a room leaves cut tiles on both sides rather than a full row on one side and a sliver on the other — which looks better but cuts more tiles. Diagonal and feature borders do the same. Whatever allowance you choose, round the final number up to whole tiles, and then up again to whole boxes, because you cannot buy part of a box. The calculator lets you dial the waste percentage up or down and re-runs instantly, so you can see the effect of a diagonal lay before you order.

5. Buying by the box, batches and spares

Tiles are sold by the box, and boxes are labelled by the area they cover rather than by a tidy round count — so the simplest way to order is to work in square feet or square metres, add your waste, and buy enough boxes to cover that area. If you would rather count tiles, the box also states how many it holds; enter that figure in the calculator and it converts your tile count into whole boxes for you.

One detail catches people out: the dye lot, or batch number. Ceramic and porcelain tiles are fired in batches, and the colour can vary subtly from one batch to the next. Buy all your tile — including the waste margin — in a single order so it comes from the same batch, and check the lot number on each box. It is also worth keeping two or three spare tiles after the job, stored flat, so that if one cracks years later you can replace it with an exact match rather than hunting for a discontinued line. That habit is the real reason a slightly generous order beats a tight one.

6. Fitting tile into the wider job

A tile estimate is only as good as the surface underneath it, so plan the substrate alongside the tile. A floor needs a flat, solid base; if you are pouring or topping a slab first, the concrete calculator works out the volume to order. For a wall, the boarding goes up before the tile, and the drywall calculator tallies the sheets — in a wet area you would specify a backer board rather than ordinary board, but the area maths is the same. You will also want adhesive and grout, both sold by coverage that depends on tile size and joint width, so check the bag for its stated coverage and apply the same round-up discipline.

Browse the other estimating tools on the tiling hub and across the site, estimate each material once with a sensible waste margin, and you will order close to right the first time — which is the whole point of working it out before you load the car.

Common questions

How do you calculate how many tiles you need?

Measure the floor or wall as length × width to get the area, add about 10% for waste, then divide by the area of one tile and round up. A 10 × 10 ft floor is 100 ft²; with 12 × 12 in tiles that is 100 tiles, or about 110 once you add the waste allowance. The same method works in metres: a 3 × 3 m floor is 9 m², which is about 110 tiles of the 300 × 300 mm size with waste.

How much tile do I need for a 10x10 room?

A 10 × 10 ft room is 100 ft². Buy about 110 ft² of tile to include a 10% waste allowance. In tiles, that is roughly 110 of the 12 × 12 in size, about 55 of the 12 × 24 in size, or about 28 of the 24 × 24 in size — round up to whole tiles and whole boxes.

How much extra tile should I buy for cuts and waste?

About 10% extra for a straight grid layout, around 15% for a diagonal layout, and up to 20% for herringbone or other complex patterns, because every angled cut creates an offcut you usually cannot reuse. It is also wise to keep a few spare tiles from the same batch for future repairs.

How many tiles are in a box?

It depends on the tile size and brand and is always printed on the box or listing — small tiles come many to a box, large-format tiles only a few. Boxes are usually labelled by the area they cover, so the simplest approach is to work in square feet or square metres, add waste, then buy enough boxes to cover that area, rounding up.