The Tile Calculator estimates how many tiles a rectangular floor needs: it divides the room's area by the tile's area, rounds up (tiles are whole), inflates the count by your waste percentage, and, if you give tiles per box, converts the result into boxes to buy. Room dimensions are in metres; tile dimensions can be entered in metres, centimetres, or inches.
How It Works
The waste is applied to the rounded base count rather than to the raw area, a small conservatism built into the calculator that occasionally adds one tile versus an area-first method, in the direction you want the error to fall.
Parameters
| Input | Required | Meaning | |---|---|---| | Room length / width | Yes | In metres | | Tile length / width | Yes | With their unit (m, cm, or in) | | Waste % | No | Default 10% | | Tiles per box | No | Enables the boxes result |
Worked example
A 4 m by 3 m room (12 square metres) with 30 cm by 30 cm tiles (0.09 square metres each): the base count is ceil(12 / 0.09) = 134 tiles, and at the default 10% waste the purchase count is 148 tiles, covering an effective 13.2 square metres. At 12 tiles per box that is ceil(148 / 12) = 13 boxes. Keep the arithmetic in view when a retailer's own estimator disagrees: the two legitimate sources of difference are the waste percentage chosen and whether waste is applied before or after rounding, worth a tile or two either way, while a disagreement of whole boxes means someone measured a different room.
Choosing the waste percentage honestly
Waste is not padding; it is the budget for cuts at every wall, breakage in handling and cutting (porcelain and large formats break more), the pattern's geometry, and future repairs. Straight grid layouts in rectangular rooms live comfortably at the default 10%. Diagonal (45-degree) layouts push cuts to every edge and want about 15%. Herringbone, chevron, and mixed patterns, small rooms with many corners and doorways, and large-format tiles (where one bad cut wastes a square metre) justify 15 to 20%. Whatever percentage you choose, buy the extra as part of the same order: dye lots and calibres vary between production runs, and the box you need in three years for a cracked tile will not match the floor if it comes from a different lot, which is the entire argument for keeping a spare box in the garage.
Grout joints, borders, and what the area method ignores
The calculator divides nominal areas, so it implicitly assumes tiles laid edge to edge: real joints (typically 3 to 5 mm on floors) spread tiles slightly, meaning the area method's count carries a small hidden surplus that partly offsets cuts, one reason the 10% default performs better in practice than spreadsheet pessimists expect. Borders, feature strips, thresholds, and skirting tiles are separate line items the calculator does not create, and rooms that are not rectangles should be decomposed into rectangles (or measured as the bounding rectangle with the waste raised), because an L-shaped room priced by its bounding box over-orders by the missing corner's area. Measure the room at several points: walls wander, and the governing dimension is the largest, since tiles must reach the far wall everywhere.
Frequently Asked Questions
Does the calculator account for grout spacing?
Not explicitly: it divides areas using the tiles' nominal dimensions. The slight spread from real grout joints works in your favour and is absorbed by the waste allowance at normal percentages.
How many spare tiles should I keep after the job?
Whatever the waste calculation left over, plus ideally one full box stored flat and dry. Repairs years later are the second purpose of the waste margin; a discontinued line with no spares turns one cracked tile into a re-flooring conversation.
The tile size I enter in centimetres gives a wild answer. What went wrong?
Unit mismatch: the room is in metres while tile dimensions take their own unit selector. Enter tile sizes with the correct unit chosen (30 means 30 m if metres is selected), and if the unit is left unspecified the calculator assumes values over 2 are centimetres, a fallback that rescues most pastes but is worth overriding deliberately.