How tiles are calculated
Each tile takes up its own size plus one grout joint in each direction. Divide the area in square inches by that footprint to get the tiles that cover the floor or wall with nothing wasted.
area (in²) = length (ft) × width (ft) × 144
tiles to cover = area (in²) ÷ ((tile length + joint) × (tile width + joint))
Then add the cut waste for the layout and round up, first to whole tiles and then to whole boxes. Waste is 10% for a straight grid or offset (brick) layout, 15% for diagonal and 20% for herringbone.
tiles to order = tiles to cover × (1 + waste %), rounded up
boxes = tiles to order ÷ tiles per box, rounded up
Thinset is counted by area. The trowel notch, and so the coverage of a 50 lb bag, follows the longest side of the tile: about 90 ft² per bag for tiles under 8 in, 60 ft² for 8–12 in and 40 ft² over 12 in.
thinset bags = area (ft²) ÷ coverage per bag, rounded up
Grout fills the joints. Per square foot there are 144 ÷ (L × W) tiles, and each tile owns one joint along its length and one along its width, as deep as the tile is thick (3/8 in assumed).
joint volume (in³ per ft²) = 144 ÷ (L × W) × (L + W) × joint × 3/8
grout (lb) = joint volume × 0.064 × area (ft²)
grout bags = grout (lb) ÷ 25, rounded up
The 0.064 lb per cubic inch is the density of grout in the joint, back-solved from the Custom Building Products sanded-grout coverage card (348 ft² per 25 lb for 12 × 12 × 3/8 in tile with 1/8 in joints). Allow a little extra for cleanup.
Worked example: 10 × 8 ft floor in 12×12 in tile
The calculator opens on a 10 × 8 ft floor in 12×12 in tile with 1/8 in joints, laid in a straight grid, with 10 tiles per box.
- Area: 10 × 8 = 80 ft², or 11,520 in².
- Footprint: 12.125 × 12.125 = 147.02 in². Tiles to cover: 11,520 ÷ 147.02 = 78.4.
- Waste: 78.4 × 1.10 = 86.2, so order 87 tiles, or 9 boxes of 10.
- Thinset: the longest side is 12 in, so use a 1/4 × 3/8 in notch at about 60 ft² per bag. 80 ÷ 60 = 1.33, so 2 bags.
- Grout: 144 ÷ (12 × 12) × (12 + 12) = 24 in of joint per ft². 24 × 0.125 × 0.375 × 0.064 × 80 = 5.8 lb, so 1 bag of 25 lb.
Tiles per 100 square feet
| Tile size (in) | Tiles, no waste | Tiles to order |
|---|---|---|
| 4 × 4 | 846.3 | 931 |
| 6 × 6 | 383.8 | 423 |
| 12 × 12 | 97.9 | 108 |
| 18 × 18 | 43.8 | 49 |
| 6 × 24 | 97.5 | 108 |
| 12 × 24 | 49.2 | 55 |
| 24 × 24 | 24.7 | 28 |
Thinset, trowels and grout
Bigger tile needs a deeper notch so the mortar reaches the whole back of the tile. The coverage below is for a 50 lb bag on a flat floor.
| Tile, longest side | Trowel notch | Coverage |
|---|---|---|
| under 8 in | 1/4 × 1/4 in square | 90 ft² |
| 8–12 in | 1/4 × 3/8 in | 60 ft² |
| over 12 in | 1/2 × 1/2 in | 40 ft² |
- Back-butter large-format tile (a thin skim on the back of each tile) and expect less coverage per bag than the table shows. Large tile also needs a flat substrate: 1/8 in in 10 ft.
- Pull a tile up now and then while setting. The back should be covered edge to edge, not just the ridges.
- Use unsanded grout for joints under 1/8 in and sanded grout for 1/8 in and wider.
- Only rectified tile, which is ground to an exact size, can take a 1/16 in joint. Standard tile varies a little in size and needs 1/8 in or more to keep the lines straight.
Measuring and layout tips
- Measure wall to wall at the widest points. For an L-shaped room, split it into rectangles and enter each one with “+ Add another area”; the areas are added before the waste and the tile and box counts are rounded once.
- For a wall, enter the wall width and the tiled height. Subtract large openings such as windows by running them separately; small cut-outs come out of the waste allowance.
- Snap centre lines and lay out from the middle so the cuts at opposite walls match. The diagram shows the default floor laid this way.
- Diagonal and herringbone layouts cut every edge tile. That is why they carry 15% and 20% waste instead of 10%.
- Buy all the tile at once and check that every box carries the same lot or shade number. Keep a few spare tiles for repairs.
Sources
- Tiles: area ÷ (tile + joint) footprint, plus pattern waste (straight/offset 10%, diagonal 15%, herringbone 20% — industry norms)
- Thinset (50 lb bag) coverage by notch (manufacturer typical): 1/4 × 1/4 in square notch ≈ 90 ft² for tiles under 8 in; 1/4 × 3/8 in ≈ 60 ft² for 8–12 in; 1/2 × 1/2 in ≈ 40 ft² for large format over 12 in (back-buttering reduces further)
- Grout: joint volume per ft² = 144/(L×W) × (L+W) × gap × thickness (3/8 in default tile thickness) in³; multiplied by 0.064 lb/in³, the density implied by the Custom Building Products Polyblend Plus sanded grout coverage card. 25 lb bags.
- Custom Building Products VersaBond thinset coverage chart (1/4 × 1/4 in and 1/4 × 3/8 in notches); Schluter (1/2 × 1/2 in notch, 30–40 ft² per 50 lb)