Tile Calculator: How Many Tiles Do I Need?

This tile calculator works out how many tiles and boxes you need for a floor, wall or backsplash, based on the area, the tile size, the grout joint width and a waste allowance. It answers the question “how many tiles do I need?” with a number you can take straight to the store.

Tile Calculator

Estimates only. Check product labels and local conditions before buying.

How to Use the Tile Calculator

  1. Measure the length and width of the area you are tiling in feet. For a wall, use the wall width and the height you plan to tile.
  2. Enter the tile width and tile length in inches, using the nominal size on the box (for example 12 x 24).
  3. Choose the grout joint width you plan to use. 1/8 inch is common for rectified porcelain; wider joints suit handmade or uneven tile.
  4. Pick a waste allowance: 5% for a simple square room, 10% for a typical job, 15% for a diagonal layout, or 20% for complex patterns.
  5. Enter the number of tiles per box from the product label, then read the tiles and boxes to buy.

How the Calculation Works

The calculator first finds the area to tile by multiplying length by width in feet. It then works out how much area each tile actually covers once the grout joint is included. The joint width is added to both the tile width and the tile length, the two are multiplied, and the result is divided by 144 to turn square inches into square feet.

The area is divided by that coverage per tile to get the number of tiles before waste. This number is multiplied by 1 plus the waste percentage and rounded up to a whole tile. Finally, the tile count is divided by the tiles per box and rounded up to a whole box. If you leave tiles per box blank, only the tile count is shown.

Worked example with the default values: an 8 x 5 foot area, 12 x 24 inch tiles, a 1/8 inch (0.125 inch) grout joint, 10% waste and 8 tiles per box.

  • Area to tile: 8 x 5 = 40 square feet
  • Tile size with joint: 12.125 x 24.125 = 292.52 square inches
  • Coverage per tile: 292.52 / 144 = 2.031 square feet
  • Tiles before waste: 40 / 2.031 = 19.69, shown as 20
  • With 10% waste: 19.69 x 1.10 = 21.66, rounded up to 22 tiles
  • Boxes: 22 / 8 = 2.75, rounded up to 3 boxes

Switching to the 15% diagonal allowance gives 19.69 x 1.15 = 22.64, or 23 tiles, which still fits in 3 boxes.

Tiles per Square Foot by Common Tile Size

The table shows roughly how many tiles cover one square foot and how many you need per 100 square feet before waste, using a 1/8 inch grout joint. Mosaic tiles are usually sold on mesh sheets, so buy those by the square foot instead.

Tile size Coverage per tile with 1/8 in joint Tiles per 100 sq ft before waste
3 x 6 in subway 0.133 sq ft about 753
4 x 4 in 0.118 sq ft about 847
6 x 6 in 0.261 sq ft about 384
12 x 12 in 1.021 sq ft about 98
12 x 24 in 2.031 sq ft about 50
18 x 18 in 2.281 sq ft about 44
24 x 24 in 4.042 sq ft about 25
6 x 36 in plank 1.537 sq ft about 65

Tips and Common Mistakes

  • Measure each section separately. For an L-shaped floor or a backsplash broken up by windows, calculate each rectangle on its own and add the tile counts, or run the calculator once per section.
  • Do not skimp on waste. Cuts at walls, around toilets and at doorways use up more tile than people expect. Large format tile and diagonal or herringbone layouts produce more offcuts.
  • Keep spare tiles. A few extra tiles from the same batch make future repairs much easier, since a discontinued tile or a different dye lot can be hard to match.
  • Check the dye lot or shade number. Buy all boxes at once and confirm they share the same lot number. Mix tiles from several boxes as you lay them to blend small color differences.
  • Use the actual tile size if it differs. Some tiles labeled 12 x 24 measure slightly less. If the box lists an exact size, enter that for a closer count.
  • Remember the other materials. Thinset, grout, spacers, backer board and trim pieces are not included in this tile count. Bullnose or edge trim is usually bought by the linear foot.
  • Prep matters more than math. A flat, stable surface is essential for large tiles. Uneven floors cause lippage that no amount of extra tile will fix.

Frequently Asked Questions

How many tiles do I need for a 5 x 8 bathroom floor?
A 5 x 8 foot floor is 40 square feet. With 12 x 24 inch tiles, a 1/8 inch joint and 10% waste, you need about 22 tiles. Subtract the area under a tub or vanity if the tile will not go there.

How much extra tile should I buy?
A common rule of thumb is 10% extra for a standard straight layout, 15% for diagonal layouts, and up to 20% for herringbone or rooms with many angles and cuts. Simple square rooms can sometimes get by with 5%.

Does grout width really change the tile count?
Slightly. Wider joints mean each tile covers a bit more area, so you need fewer tiles. The effect is small for large tiles but becomes noticeable with small tiles like 4 x 4 or mosaics.

Can I return unused boxes of tile?
Many stores accept unopened boxes, but policies vary and special order tile often cannot be returned. Ask before you buy, and consider keeping one spare box for repairs.

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