Tile Calculator — How Many Tiles and Boxes to Buy

How the tile count works

Area to tile. Multiply length by width for each part of the floor or wall, add them, and subtract anything you will not tile — a tub, a kitchen island, a window. A 12 × 10 ft floor is 120 ft².
Area one tile covers. Add the grout joint to the tile’s length and width: a 12-inch tile with a 1/8-inch joint takes up 12.125 × 12.125 = 147.0 in², or 1.021 ft².
Tiles. 120 ÷ 1.021 = 117.5, rounded up to 118.
Waste. Add 10%: 118 × 1.10 = 129.8, rounded up to 130.
Boxes. 130 ÷ 10 per box = 13 boxes.

The calculator shows each step with your numbers, the spare tiles left in the last box, and the cost per tile, per box or per square foot. Metric works the same way, with the joint in millimeters.

Tiles per square foot

Tile size	Tiles per ft²	Tiles per 100 ft²
3 × 6 in (subway)	7.52	753
4 × 4 in	8.46	847
6 × 6 in	3.84	384
12 × 12 in	0.98	98
12 × 24 in	0.49	50
18 × 18 in	0.44	44
24 × 24 in	0.25	25

All with a 1/8-inch joint and before waste. Small tiles are sold on mesh sheets — for those, enter the sheet as the “tile” and sheets per box.

How much extra to buy

Cuts at walls, corners and doorways leave offcuts too small to reuse, and some tiles crack. The usual allowance is 5% to 10%; use the upper end, or more, for rooms with many corners, for diagonal and herringbone patterns, and for large-format tiles where each cut wastes more. Buy whole boxes, and keep a few spare tiles after the job: a replacement from the same production lot will match in shade and size, while a later batch may not.

Measuring floors, walls and backsplashes

Measure in feet and inches and convert to decimal feet — 10 ft 6 in is 10.5 ft; the feet and inches calculator adds up awkward lengths. Floors: split L-shaped rooms into rectangles and leave out cabinets and tubs, which are not tiled underneath. Walls and showers: multiply the height to be tiled by the width of each wall and leave out windows and niches. Backsplashes: the length of the counter run times the height up to the cabinets, minus the window. For the area of other shapes — circles, triangles — use the square footage calculator.

Grout joints and layout

The joint width depends on the tile: check the box or the manufacturer’s sheet for the recommended size, since edges that are cut very straight allow narrow joints and handmade tiles need wider ones. Wider joints mean slightly fewer tiles for the same area and more grout. Before you start, lay a row of tiles dry along the longest wall to see where the cuts fall; centering the layout avoids thin slivers at one wall. For the paint on the walls above the tile, see the paint calculator.

Frequently asked questions

How do I calculate how many tiles I need?

Divide the area by the area one tile covers including its grout joint, round up, then add a waste allowance. 120 ft² ÷ 1.021 ft² per 12-inch tile with a 1/8-inch joint is 117.5, so 118 tiles, or 130 with 10% extra.

How much extra tile should I buy?

Most guides, including the leading online tile calculator, suggest 5% to 10% more for cuts and breakage. Rooms with many corners, diagonal or herringbone layouts, and large tiles waste more, so set a higher allowance for those.

How many 12 × 12 tiles are in a square foot?

Just under one: with a 1/8-inch joint each tile covers 1.021 ft², so 100 ft² needs 98 tiles before waste.

Should I count the grout lines?

Yes. Each tile plus its joint takes up a slightly larger square, so ignoring the joint overestimates the count a little — about 2% for 12-inch tiles and 1/8-inch joints, more for small tiles.

How do I measure a room with a tub or cabinets?

Measure the whole room as a rectangle, then add the tub, island or cabinet base as an area to leave out. For an L-shaped room, split it into two rectangles.

Why buy a few spare tiles?

To replace a cracked tile later with one from the same production lot. Tiles from a different lot can differ in shade and size.