Tile Calculator (tiles and boxes needed)

Work out how many tiles and boxes a floor or wall needs, including the grout gap and a waste allowance for cuts.

Boxes to buy–

Tiles to buy–

Tiles for the bare area–

Area to cover–

Each tile covers–

Spare tiles left over–

Keep the spares. Tiles are made in batches and a replacement bought later will rarely be quite the same shade.

Tiles per 100 ft² by size

The bare count, and what to buy allowing a 1/8 in grout gap and 10% for cuts. Big tiles mean fewer pieces but more waste per cut, which is why the allowance matters more as the format grows.

Tile size	Bare count	With gap + 10%
4 × 4 in	900	935
6 × 6 in	400	424
12 × 12 in	100	108
18 × 18 in	44.444	49
24 × 24 in	25	28
12 × 24 in	50	55
3 × 6 in subway	800	831

Working out tile quantities

Divide the area you are covering by the area one tile covers, then add enough for the pieces you will cut and break. The second step is not optional — a tiled floor with no offcuts does not exist, and running out halfway through means matching a dye lot you can no longer buy.

Tiles = area / ((tile width + gap) × (tile height + gap)) × (1 + waste)

Why the grout gap is in there

Each tile effectively occupies its own size plus one grout joint, because every tile owns the gap on two of its four sides. On 12 inch tiles with a 1/8 inch joint the effect is small — about 2% fewer tiles. On 1 inch mosaic with the same joint it is enormous, well over 20%. Ignoring the gap always makes you over-order, which is the safe direction, but on a large mosaic job it is money left on the counter.

Worked example

A 12 × 10 ft floor is 120 ft². In 12 inch tiles with a 1/8 inch joint, each tile covers 12.125 × 12.125 in = 147 in², so 120 ft² (17 280 in²) needs about 117.5 tiles. A straight lay in a simple room takes 10% for cuts, giving 130 tiles — eleven boxes of twelve, with two spare.

How much waste to allow

Ten percent covers a straight lay in a square room. Fifteen is safer where there are alcoves, pipe boxings, or a lot of edges to cut around. A diagonal layout wants twenty, because every tile at the perimeter is cut on an angle and the offcut is rarely usable elsewhere. Herringbone and chevron want twenty-five for the same reason, compounded. If your tiles have a strong directional pattern, add more still — you cannot always rotate a cut piece to fit.

Buy by the box, and buy the spares

Tiles are sold in boxes, so the real answer is always rounded up to a whole box — this calculator does that and tells you how many spares you end up with. Keep them. Ceramic and porcelain are fired in batches and the shade varies noticeably between them, so a tile bought in two years to replace a cracked one will not match. A few spares in the loft is cheap insurance.

For an L-shaped or irregular room, work out the area in sections with thearea calculator and add them together before entering it here.