Tiles fail orders in two directions: the box you are short of on the last row — from a dye lot that no longer exists — and the three boxes that live in the garage forever. This tile calculator works from the three numbers that decide both: the area to cover, the tile’s real size, and a waste percentage matched to your layout. It returns the tiles to buy and, from your box’s stated coverage, the boxes to order. It is built for bathrooms (floor plus tiled walls are just two areas to add together) but the arithmetic is the same for any room.
Worked example — a small bathroom floor
Floor 3 m × 2.5 m = 7.5 m², tiles 30 × 30 cm (0.09 m² each), waste at 10% for a straight grid: the area to buy for is 7.5 × 1.10 = 8.25 m², so tiles = ceil(8.25 ÷ 0.09) = 92 tiles. With boxes covering 1.2 m² each, boxes = ceil(8.25 ÷ 1.2) = 7 boxes. Notice the two roundings stack — 92 tiles is 8.28 m² of tile and 7 boxes is 8.4 m² — which is normal and healthy: whole boxes are the unit you can actually buy, and the leftover part-box is your breakage stock for the next decade.
Setting the waste percentage
Waste is layout, not luck. Straight grid in a rectangular room: 10% is the trade standard. Diagonal (diamond) layouts: 15%, because every edge tile is a cut. Herringbone and large-format tiles in small rooms: 15–20% — a 60 × 60 tile in a 1.2 m wide bathroom throws away a third of some rows. Broken-bond brick patterns sit around 12–15%. If your percentage feels like a guess, it is cheaper to guess one box high than to re-order into a different dye lot: tile shades genuinely vary between production batches, and the difference shows most on the wall you look at in the bath.
Measuring the area honestly
For a floor, length × width of the room, minus nothing — tile goes under the bath panel and behind the toilet more often than not. For walls, measure each wall you will actually tile (a splashback zone is not a wall) and add the areas into the calculator one run at a time, or sum them first. Around a bath or shower tray, deduct the tray, not the bath. And measure the tile itself with a tape: a “30 cm” tile that is really 29.7 cm changes the count by 2% before you start.
About grout — the honest note
Grout consumption is not a fixed percentage of anything: it depends on tile size, joint width, joint depth and tile thickness together, which is why this calculator flags it instead of faking a number. As orientation only: a floor of 30 × 30 cm tiles with 3 mm joints typically takes roughly 0.3–0.5 kg of grout per m²; small mosaics with wide joints can take three times that. If grout is the number you need exactly, our Spanish companion tool calculates it from all four inputs. Buy grout from one batch too, and keep the bag — the colour code on it is how you match a repair in five years.
One more variable: the tile itself
Two costs hide in the tile size you pick. The first is cutting: the closer the tile module sits to a divisor of the room’s dimensions, the fewer cuts and the less waste — a 33 × 33 cm tile in a 2.64 m wide bathroom wastes almost nothing, where a 45 cm tile sheds a strip off every row. If you are between two favourite tiles, run both through the calculator at the same waste percentage and then at a percentage 5 points higher for the awkward one; the comparison is the honest price of the prettier grid. The second is weight: a box of large-format porcelain can weigh 25–30 kg, and seven boxes up two flights of stairs is a real consideration for a solo installer. The calculator counts tiles, but let the box weight it implies decide whether you order a delivery or a workout.
Related tools
Versión en español: Calculadora de Azulejos y Desperdicio para Baño: piezas y cajas para piso y paredes · Grout Calculator (in Spanish) · Baseboard Calculator.
Embed this tool on your website — free
Copy the code below to add this working tool to your own page. A small credit link stays with it — that’s all we ask.
Pingback: Baseboard Calculator — Room Perimeters Minus Door Openings, Pieces by Board Length