Tile Calculator: How Many Tiles Do I Need, Plus Grout

Tile shortages almost never come from bad measuring. They come from cuts: every edge, alcove and pipe run turns a full tile into an offcut you cannot use anywhere else. This calculator takes your area and tile size, adds a wastage allowance, then works out tiles, boxes, adhesive and grout together. The pattern worth knowing before you buy: large-format tiles swallow adhesive and barely touch the grout, while small mosaics and metros do the opposite.

Wastage of 10% is the standard allowance for a straight lay in a reasonably square room. Push it to 15% if you are laying diagonally, in herringbone, or into a room full of cuts: an awkward bathroom with a boxed-in soil pipe, a shower tray and a doorway can eat that much on its own. Large-format tiles need more too, because a single bad cut writes off a much bigger piece.

How to measure the area

Measure each surface separately and add the figures together rather than trying to average a room. For a floor, length times width is enough. For walls, measure each wall's width by the height you intend to tile, which is often not the full ceiling height: half height, a metre above a bath, or three courses behind a worktop are all common. If you are tiling several walls, switch the surface selector to "I already know the area" and enter the total.

Only deduct openings that are genuinely large, roughly a square metre or more, such as a window, a shower tray or a bath panel run you are not tiling. Small deductions are false economy because the offcuts around a door or a socket rarely give you a usable full tile, and taking them off the total is how people end up half a box short on the last day.

Buying: boxes, batches and spares

Tiles are sold by the box, so your real order is always rounded up, and box counts vary by range: check the box or the product page for tiles per box before you rely on a price per square metre. Order the whole job in one go and check that every box carries the same batch or shade number. Colour shifts between production runs are normal, and a top-up box bought a month later can land noticeably different, which shows most on plain matt tiles and warm neutrals. Keep a few spares in the loft for cracked tiles and future plumbing work.

Adhesive and grout are estimates

The adhesive figure assumes a cement-based powder adhesive on a flat, solid substrate, with the notch size stepping up as tiles get bigger. An uneven wall or floor can push usage well past it, and large-format tiles usually need back-buttering to hit the coverage that porcelain requires, so treat the bag count as a starting point and read the coverage printed on the bag. Grout is worked out from your tile size, joint width and tile thickness, which is why a 600 mm tile with 3 mm joints needs so little of it, and mosaics or metros need several times as much over the same area.

Once you know the tile quantity, the rest of the room budget is easier to pin down: see our paint quantity calculator for the decorating side, our bathroom worktops guide for surfaces that sit against the tiling, and the London renovation cost calculator if you are pricing the whole project. For colour direction, our guide to beige bathroom tiles covers the warm neutrals that have replaced grey.