Calculate how many tiles and boxes you need for any floor or wall project, including grout joints, waste allowance, cost, adhesive, and grout.
Tile Formula
When you solve for tiles needed, the calculator first turns each tile into a module that includes the grout joint, then divides the tiled area by that module and applies a waste allowance for cuts and breakage.
M = (t_l + g) * (t_w + g) / 144
A = (L * W) - Openings
N = roundup( A * (1 + w) / M )
Boxes = roundup( N / tiles_per_box )
When you solve for coverage from tiles on hand, the calculator multiplies the number of tiles by the same module area to get gross coverage, then divides by the waste factor to show the practical area you can expect to finish.
Coverage_gross = Q * M
Coverage_net = Coverage_gross / (1 + w)
- M = area of one tile including its grout joint (square feet; divide by 10000 instead of 144 in metric mode)
- t_l, t_w = tile length and width (inches, or centimeters in metric mode)
- g = grout joint width in the same units as the tile
- A = the area you are tiling after subtracting any openings
- L, W = length and width of the area (feet, or meters in metric mode)
- w = waste allowance as a decimal (10 percent = 0.10)
- N = whole tiles to buy
- Q = tiles you already have on hand
The grout joint is added to both tile dimensions because each tile occupies its own size plus part of a joint on every edge, so a wider joint means each tile covers slightly more area and you need fewer of them. The waste allowance raises the count to cover cut pieces, mistakes, and future repairs, and every result rounds up to whole tiles and whole boxes because you cannot buy a fraction of either.
Waste Allowance and Coverage Reference
The layout you choose sets how much extra tile to add. Diagonal and interlocking patterns produce more cut waste than a simple straight grid.
| Layout | Typical waste allowance |
|---|---|
| Straight set (grid) | 10 percent |
| Offset / running bond | 15 percent |
| Diagonal or herringbone | 20 percent |
| Rooms with many corners or jogs | Add 5 percent on top |
Use this second table to sanity check the tile count. It shows how many tiles of each size cover 100 square feet with a 1/8 inch joint, before waste is added.
| Tile size | Tiles per 100 sq ft (no waste) |
|---|---|
| 3 x 6 in subway | 753 |
| 4 x 4 in | 846 |
| 6 x 6 in | 384 |
| 12 x 12 in | 98 |
| 12 x 24 in | 49 |
| 18 x 18 in | 44 |
Example Problems
Example 1: tiles needed. You are tiling a floor that is 12 ft by 10 ft, which is 120 square feet. You choose 12 x 12 in tiles with a 1/8 inch grout joint in a straight set, so the waste allowance is 10 percent. The module area is (12.125 x 12.125) / 144 = 1.021 sq ft. Tiles needed = roundup(120 x 1.10 / 1.021) = roundup(129.3) = 130 tiles. If each box holds 10 tiles, you need roundup(130 / 10) = 13 boxes.
Example 2: coverage from tiles on hand. You have 200 tiles that are 12 x 24 in with a 1/8 inch joint, and you plan a running bond at 15 percent waste. The module area is (12.125 x 24.125) / 144 = 2.031 sq ft. Gross coverage = 200 x 2.031 = 406.3 sq ft. Practical coverage after waste = 406.3 / 1.15 = 353.3 sq ft.
Frequently Asked Questions
How much extra tile should you buy? Add 10 percent for a straight layout, 15 percent for an offset pattern, and 20 percent for diagonal or herringbone work. Buying a little extra also leaves you with spare tiles from the same batch, which is useful for future repairs because dye lots change between production runs.
Does the grout joint change how many tiles you need? Yes. The joint is added to each tile dimension, so a wider joint makes every tile module larger and lowers the total count. The effect is small for big tiles and a tight joint, but it becomes noticeable with small mosaics or wide joints, which is why the calculator includes the joint in the module area.
How do you find the area of an odd-shaped room? Split the floor or wall into rectangles, multiply length by width for each rectangle, and add the results to get the total area. Enter that figure using the known total area option, then use the openings field to subtract doorways, niches, or fixtures that will not be tiled.
