How many tiles do I need for a floor?

Tiles are bought by the box and cut by the piece, so the number that matters is boxes rounded up — not area divided by tile size. This calculator converts the room dimensions and tile size into tiles, adds a cut allowance, and rounds to whole boxes.

Room length (ft)

Room width (ft)

Tile length (in)

Tile width (in)

Cut allowance (%)

10% straight lay, 15% diagonal, more for patterned layouts.

Tiles per box (count)

Tiles needed

132tiles

Boxes to buy 14 boxesFloor area 120.0 sq ft

Assumes a rectangular room and a rectilinear layout. Herringbone, chevron and patterned installations can waste 20-25%, and rooms with many angles should be split into rectangles.

The cut allowance is the part most people get wrong. A straight lay in a rectangular room reaches the walls with a row of cut tiles on two sides, and cut tiles come out of full ones: even a perfect install wastes 5%. Ten percent is the right default for a straight lay, fifteen for a diagonal or herringbone layout, and twenty or more for a large-format tile in a room with many corners, because a single bad cut can consume a whole tile.

Room measurement is the other half. Measure to the nearest quarter inch at several points and use the largest figure, since rooms are rarely square — a 12 × 10 ft room can be 10 ft 1 in at one end. For a bathroom, measure under the toilet and vanity, because tiling around them properly needs more cuts, not less material.

How the calculation works

Tiles = ceil(room length × room width × (1 + waste ÷ 100) ÷ tile area), where tile area = (tile length ÷ 12) × (tile width ÷ 12) in square feet. Boxes = ceil(tiles ÷ tiles per box).

Rounding up happens twice, and both times it matters: a partial tile is a cut tile, and a partial box is a full box's worth of money.

• Floor area is a rectangle of the entered dimensions. Alcoves and closets should be calculated separately and added.
• Tiles are laid with grout joints; a 3 mm joint on a 12 in tile adds roughly 2% to the coverage, which the cut allowance absorbs.
• The cut allowance covers breakage during cutting and pattern matching; it is not a stock allowance for future repairs, which is usually worth one extra box.
• Tile thickness, adhesive and backer board are not included.

Sources: Tile coverage = (tile length in / 12) × (tile width in / 12) square feet; Cut allowances: 10% straight lay, 15% diagonal, 20%+ patterned (tiling trade guidance)

Worked examples

Questions

How many 12 × 12 tiles do I need for 100 square feet?

Around 110 with a 10% cut allowance, since each tile covers a square foot. In boxes of 10, that is 11 boxes.

How much extra tile should I buy?

Ten percent for a straight lay in a simple room, fifteen for diagonal, twenty for a busy layout or large-format tiles. Buy one spare box regardless if the tile is a colour you might need to match later.

Do I count the space under cabinets and the toilet?

For a bathroom, yes — the floor still has to be tiled under a toilet that will be lifted to fit it, and cutting around a fixed cabinet wastes more tile than tiling under it.

Does grout width change the number of tiles?

Slightly. Wider joints mean fewer tiles, because each tile plus its joints covers more area. The difference is under 3% at normal joint widths and is absorbed by the cut allowance.

How many tiles are in a box?

It varies by manufacturer and tile size — commonly 10 to 15 for 12 in tiles, fewer for large-format. The figure is printed on the box and is an input here for that reason.

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Written and maintained by Sam Winters. Last updated 2026-11-04. Every figure is computed in your browser; nothing you enter is sent anywhere. Found an error? Tell me — accuracy reports get fixed first.