Step 1: measure the area
Multiply length by width for each rectangular section and add them together. Our own arithmetic: a 10 by 8 ft floor is 80 sq ft. Measure walls the same way, height by width, and subtract any large opening.
Step 2: add extra for cuts and breakage
Daltile, a tile maker, says it highly recommends buying approximately 10 percent more tile than you expect to need. Bob Vila gives the same minimum and says up to 20 percent for a herringbone or diagonal offset. One tile retailer lists straight lay at 10 percent, diagonal and herringbone at 15 to 20 percent and large format (12 by 24 inches or bigger) at 15 percent. Another says to bump up to 15 percent for diagonal or intricate layouts.
Sources are not uniform: one retailer suggests as little as 5 to 7 percent for a straight lay and another as much as 20 percent. The calculator uses 10 percent straight, 15 percent diagonal, 20 percent herringbone and 15 percent large format, and you can change the figure.
Step 3: turn square feet into tiles
Divide the square feet to buy by the area of one tile. Our own arithmetic: 12 by 12 in is 144 sq in, which is 1 sq ft; 12 by 24 in is 2 sq ft; 24 by 24 in is 4 sq ft; a 4 by 4 in tile is 0.111 sq ft (9 per sq ft); a 3 by 6 in subway tile is 0.125 sq ft (8 per sq ft).
Worked example: 80 sq ft x 1.10 = 88 sq ft. With 12 by 24 in tiles (2 sq ft each) that is 44 tiles. With a herringbone pattern at 20 percent: 80 x 1.20 = 96 sq ft, or 48 tiles.
Step 4: round up to whole boxes
Tile is sold by the box and coverage differs by product, so read the box label. Example only: at 10 sq ft per box, 88 sq ft is 8.8 boxes, so buy 9. Tile Shoppes advises always rounding up to the full box.
Keep a spare box
Daltile explains that keeping extra tile from the same dye lot lets you replace broken tiles later, because the dye lot and printing process can change slightly over the years. Flooring Clarity suggests storing at least one full box for a small room and two or more for a large room or highly variable tile. Buy everything at the same time.
How many tiles for common areas
Each row adds 10% for a straight layout. Tile counts divide the square feet to buy by the size of one tile: 12 x 12 in is 1 sq ft, 12 x 24 in is 2 sq ft and 24 x 24 in is 4 sq ft. Change any number in the tile calculator.
| Area | Sq ft | Sq ft to buy | 12 x 12 tiles | 12 x 24 tiles | 24 x 24 tiles |
|---|---|---|---|---|---|
| 5 x 8 ft area | 40 | 44 | 44 | 22 | 11 |
| 8 x 10 ft area | 80 | 88 | 88 | 44 | 22 |
| 10 x 10 ft area | 100 | 111 | 111 | 56 | 28 |
| 12 x 12 ft area | 144 | 159 | 159 | 80 | 40 |
| 12 x 16 ft area | 192 | 212 | 212 | 106 | 53 |
| 16 x 20 ft area | 320 | 352 | 352 | 176 | 88 |
Frequently asked questions
How much extra tile should I buy?
Daltile recommends about 10 percent extra. Retailers suggest 15 to 20 percent for diagonal or herringbone layouts, and 15 percent for large format tile.
Why do tile sources disagree on waste?
Rooms with many cuts, small rooms and patterned layouts waste more. Sources range from about 5 to 7 percent for a simple straight lay to 20 to 30 percent for diagonal or herringbone, so treat the figures as a guide and ask your installer.
Should I keep leftover tile?
Yes. Daltile says tile from the same dye lot is needed to replace broken tiles later, because later batches can look slightly different.
Sources: Daltile: tile FAQ, Tile Shoppes: the 10% waste rule, Bob Vila: how much tile do I need, CLE Tile: how much extra tile to buy, Flooring Clarity: how much overage tile. Read 7 November 2026.
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