Tile Calculator
Boxes, adhesive and grout — all three, from one measurement.
Estimates only. Textured walls, high ceilings, sprayers and major colour changes can all increase the amount you need. Always buy slightly more than the calculation suggests.
Tiles and grout for common jobs
| Area | Surface | Tile size | Tiles | Boxes | Tile cost |
|---|---|---|---|---|---|
| Small bathroom floor, 40 sq ft, 12x12 | 40 sq ft | 12" × 12" | 44 | 5 boxes | $175 |
| Large bathroom floor, 80 sq ft, 12x24 | 80 sq ft | 12" × 24" | 46 | 5 boxes | $175 |
| Kitchen backsplash, 30 sq ft, 3x6 | 30 sq ft | 3" × 6" | 264 | 27 boxes | $945 |
| Shower walls, 100 sq ft, 12x24 | 100 sq ft | 12" × 24" | 58 | 6 boxes | $210 |
| Hallway floor, 60 sq ft, 18x18 | 60 sq ft | 18" × 18" | 31 | 4 boxes | $140 |
| Large kitchen floor, 200 sq ft, 24x24 | 200 sq ft | 24" × 24" | 55 | 14 boxes | $490 |
Straight lay at 10 % waste unless stated. Box counts assume 10 tiles per box — always check the box your supplier stocks, because large-format tile often comes 4 or 6 to a box.
What this calculator works out
Tiling a surface needs four separate purchases, and most people only budget for the first one.
- Tiles. The area to cover, divided by the area of one tile, plus a waste allowance for cuts and breakage.
- Boxes. Tiles are sold by the box, and boxes are never split. The calculator rounds up to whole boxes.
- Adhesive. Thinset mortar is sold in 50 lb bags, and how far a bag goes depends entirely on the trowel you use.
- Grout. Sold by weight, and the amount depends on the size of the tile, the width of the joint and the thickness of the tile.
The result panel shows all four, with the cost of each.
Choosing the right waste allowance
The waste allowance is the percentage of extra tile you buy to cover cuts, breakage and mistakes. It is not optional, and it is not the same for every job.
- 10 % — straight lay. A simple grid, square to the walls. The least wasteful layout.
- 15 % — diagonal. Tiles turned 45 degrees. Every edge cut is a triangle, and the offcuts are unusable.
- 20 % — herringbone, chevron or complex patterns. Also worth 20 % for rooms with many corners, alcoves or pipes to cut around.
Buy the waste allowance even if you are confident. Tile is made in dye lots, and a second batch bought three weeks later can be visibly different. The spare tiles also become your repair stock for the next twenty years — matching a broken tile later is impossible without them.
Grout: the number nobody expects
Grout is the item that most often sends people back to the shop, because the amount depends on something counter-intuitive: smaller tiles need dramatically more grout.
Grout fills joints, and joints are the gaps between tiles. Halve the tile size and you have four times as many tiles — which means roughly four times as much joint to fill. A 2×2 mosaic floor can need six times the grout of the same area in 12×12 tile.
Three things increase grout use:
- Smaller tiles — far more joints per square foot.
- Wider joints — the width of the gap scales the volume directly.
- Thicker tiles — deeper joints hold more grout.
The calculator works all of this out from the joint volume, which is why it asks you for the joint width and the tile thickness rather than guessing.
Frequently asked questions
How many boxes of tile do I need?
Divide the area to cover by the area of one tile, add your waste allowance, then divide by the number of tiles in a box and round up. A 40 sq ft bathroom floor in 12x12 tile with 10 % waste needs 44 tiles, which is 5 boxes at 10 per box.
What waste allowance should I use for tile?
10 % for a straight lay, 15 % for a diagonal layout and 20 % for herringbone or a room with many cuts. Never buy zero waste — you need spare tiles for future repairs.
How much grout do I need?
It depends on tile size, joint width and tile thickness, because grout fills the joint volume. Smaller tiles need far more grout: a 2x2 mosaic can need six times as much as 12x12 over the same area.
How much adhesive do I need for tile?
A 50 lb bag of thinset covers about 95 sq ft with a 1/4" trowel on a flat substrate, around 80 sq ft in typical conditions, and only 60 sq ft with a 1/2" trowel for large-format tile.
How many spare tiles should I keep?
Keep a full box, or at least the leftovers from the last box. Tile is made in dye lots, so tiles bought later will not match the ones already on the wall.