Estimate how many tiles — and optional boxes — you need to cover a floor, wall, roof, or other surface. Enter tile size, the area (or length and width), and the grout gap or overlap. Results include a 5–10% extra for cuts and waste, plus an optional material-cost estimate.
Formula
Lengths convert through metres (1 in = 0.0254 m, 1 ft = 0.3048 m). Each tile covers a module of tile + gap on both sides. Tiles are the area divided by that module, rounded up.
module = (tile_length + gap) × (tile_width + gap)
tiles = ceil(area / module)
boxes = ceil(tiles / tiles_per_box)
A positive gap is grout; a negative gap is overlap. Extra for waste is applied to the unrounded tile count, then rounded up:
tiles_5% = ceil(area / module × 1.05)
tiles_10% = ceil(area / module × 1.10)
Typical 12×12 in tile with ¼ in grout
| Room | Area | Tiles | +5% | +10% | Boxes of 12 |
|---|---|---|---|---|---|
| 10 ft × 10 ft | 100 sq ft | 96 | 101 | 106 | 8 |
| 20 ft × 15 ft | 300 sq ft | 288 | 303 | 317 | 24 |
| 6 m × 4 m, 30 cm tile, 5 mm gap | 24 m² | 258 | 271 | 284 | 26 of 10 |
Floor and wall tile usually sit on a grout joint from 1/16 in to 1/2 in. Rectified tiles can use a tighter joint. Roofing tile and siding overlap instead — enter a negative gap.
Examples
Default 20 ft by 15 ft room
A 20 ft × 15 ft floor is 300 square feet. With 12×12 in tile and a ¼ in grout line, each tile covers 12.25×12.25 in (about 1.042 sq ft), so you need 288 pieces, or 24 boxes of 12. Plan on 303–317 tiles (26–27 boxes) so you have extras for cuts and a matching repair later.
30 cm tile on a 6 m by 4 m floor
A 6 m × 4 m room is 24 m². 30×30 cm tiles with a 5 mm grout line cover 0.305×0.305 m each, so you need 258 pieces. In boxes of 10 that is 26 boxes, or 28–29 boxes with 5–10% extra (271–284 tiles).