Reference
Tile sizes and grout joint widths
Tile format decides three things at once: how many tiles cover a square foot, how wide the grout joint has to be, and which trowel spreads the thinset. Get the joint wrong and a large-format floor will show every high corner. Here is each figure, and the rule behind the joint width.
Standard tile sizes and tiles per square foot
Counts are the bare division, before joints and before waste. Joints add area at the rate of roughly 1% per sixteenth of an inch on a 12 inch tile, which is inside the waste allowance and not worth calculating separately.
| Size | Per sq ft | Per m² | Where it is used |
|---|---|---|---|
| 1 × 1 in mosaic | 144 | 1 550 | Shower floors, curved surfaces |
| 2 × 2 in mosaic | 36 | 388 | Shower floors, accents |
| 3 × 6 in subway | 8 | 86 | Walls, backsplashes |
| 4 × 4 in | 9 | 97 | Backsplashes, older bathrooms |
| 6 × 6 in | 4 | 43 | Walls, small floors |
| 4 × 12 in | 3 | 32 | Walls, stacked or offset |
| 8 × 8 in | 2.25 | 24 | Floors, patterned encaustic |
| 12 × 12 in | 1 | 11 | The long-standing floor default |
| 12 × 24 in | 0.5 | 5.4 | The current floor default |
| 18 × 18 in | 0.44 | 4.8 | Floors |
| 6 × 24 in plank | 1 | 11 | Wood-look floors |
| 24 × 24 in | 0.25 | 2.7 | Large-format floors |
| 24 × 48 in | 0.125 | 1.3 | Large-format, panel look |
Grout joint widths by tile format
Joint width is not a style choice on larger tiles. It is set by how much the tiles vary from each other, and industry practice puts the joint at no less than three times that variation — a joint narrower than the tolerance has nowhere to absorb the difference, so it shows up as lippage instead.
| Tile | Joint | Grout | Note |
|---|---|---|---|
| Mosaic on sheets | 1/16 in | Unsanded | Set by the sheet backing |
| Rectified porcelain | 1/16–1/8 in | Unsanded to 1/8 | Machine-cut edges, tightest joints possible |
| Pressed ceramic, cushioned edge | 1/8–3/16 in | Sanded | Rounded edges need the width |
| Natural stone, gauged | 1/16–1/8 in | Unsanded | Sanded grout scratches polished stone |
| Any side 15 in or longer | 3/16 in minimum | Sanded | Unless rectified, then 1/8 in |
| Wood-look plank | 3/16 in | Sanded | Offset no more than a third of the length |
| Handmade, saltillo, rustic | 1/4–1/2 in | Sanded | Irregular tiles need a wide joint |
Unsanded grout is for joints up to 1/8 inch; sanded grout is for 1/8 inch and wider. Using unsanded in a wide joint cracks it as it shrinks, and using sanded in a narrow one simply will not pack.
Trowel size and thinset coverage
The trowel is chosen by tile size, and it sets how far a bag goes. Coverage below is per 50 lb bag of modified thinset over a flat substrate; an uneven floor eats considerably more.
| Tile | Trowel notch | Per 50 lb bag |
|---|---|---|
| Mosaic and up to 4 × 4 in | 3/16 in V-notch | 100–115 sq ft |
| 4 × 4 to 8 × 8 in | 1/4 × 1/4 in square | 90–100 sq ft |
| 8 × 8 to 12 × 12 in | 1/4 × 3/8 in square | 60–70 sq ft |
| 12 × 24 in and planks | 1/2 × 1/2 in square | 40–50 sq ft |
| Any side 15 in or longer | 1/2 × 1/2 in or 3/4 in U | 25–40 sq ft |
Anything with a side of 15 inches or more has to be back-buttered as well as trowelled, and the standard asks for 80% mortar contact in a dry area and 95% in a shower or outdoors. That doubles the mortar over a naive estimate, which is why large format runs through bags so much faster than the tile area suggests.
Waste by layout pattern
Every pattern that meets a wall at an angle throws away part of a tile at every course. The allowance is not padding — it is the offcut pile.
| Layout | Add | Why |
|---|---|---|
| Straight or stacked | 10% | Perimeter cuts only |
| Brick or offset | 10% | Half tiles at alternate courses reuse well |
| Diagonal | 15% | Every perimeter tile is cut at 45° |
| Herringbone | 15–20% | Angled cuts on all four edges of the room |
| Large format on a small floor | add 5% | Few tiles, so each cut costs proportionally more |
boxes = ⌈ tiles ÷ tiles per box ⌉
thinset bags = ⌈ area ÷ coverage for the trowel ⌉
Buy the whole job in one delivery. Tile is made in batches and the shade varies between them, so a box bought later to finish a floor will often be visibly different from the ones around it — and a dye lot number that matches is not a guarantee that the firing did.
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