How tile quantity is worked out
First the calculator finds the area you're covering in square feet. Then it works out how much space one tile takes up, including its grout joint, and divides one by the other.
The grout line matters more than people expect with small tile. On a 12 × 12 tile an eighth-inch joint changes the count by about 2 percent. On 2-inch mosaic the same joint cuts the tile you need by more than 10 percent. The calculator handles both.
Last comes waste. Every room has edges, outlets, door jambs and a toilet flange, and tiles get cut to fit around them. Some cuts break, and the odd tile arrives chipped. The waste allowance covers all of that.
How much waste to add
| Layout | Add |
|---|---|
| Straight lay, square room | 10% |
| Offset or brick pattern | 10 to 12% |
| Diagonal | 15% |
| Herringbone or chevron | 15 to 20% |
| Rooms with lots of corners | Another 5% |
Worked example: an 8 × 10 bathroom floor
- Area: 8 × 10 = 80 sq ft
- A 12 × 12 tile with a 1/8 inch joint covers about 1.02 sq ft
- 80 ÷ 1.02 = 79 tiles, rounded up
- Add 10% waste: 87 tiles
- At 10 tiles per box: 9 boxes
Tips from the tile aisle
Check the lot number on every box before you leave the store. Tile is fired in batches, and two lots of the same product can differ in shade or even size by a hair. Once the grout is in, a mixed floor is easy to spot.
If the tile might get discontinued, buy one more box than you need. Should a tile crack in five years, you'll want a true match, not a close guess.
For walls, measure each wall as its own rectangle and add them together. Leave out the area behind a tub or vanity if it won't be tiled. The square footage calculator adds up several sections at once.
Frequently asked questions
How many tiles are in a square foot?
It depends on tile size. One 12 by 12 tile covers a square foot. You need four 6 by 6 tiles, about nine 4 by 4 tiles, and eight 3 by 6 subway tiles, before grout lines.
How much extra tile should I buy?
Plan on 10 percent for a straight layout and 15 to 20 percent for diagonal or herringbone patterns. If the tile is a special order, round up to the next full box as well.
Does grout spacing change how many tiles I need?
A little. A wider joint means each tile plus its grout covers more area, so you need fewer tiles. The effect is small with large tile and much bigger with mosaics.
How do I measure an L-shaped room for tile?
Split it into two rectangles, measure each, and add the totals. Then enter the combined number as the length with a width of 1, or use the square footage calculator first.
Results are estimates for planning. Product coverage, site conditions and installation methods vary, so check manufacturer guidance before you buy.