Tile Calculator
Buy 11 boxes of tile.
| Material | Quantity |
|---|---|
| Area to tile | 120 ft² |
| With 10% waste | 132 ft² |
| Each tile covers including its joint | 1.0421 ft² |
| Tiles, exact | 116 |
| Tiles, with waste | 127 |
| Boxes of 12 | 11 |
| Grout 0.125 lb/ft² at this tile and joint | 16.5 lb (2 × 10 lb bags) |
| Thinset 1/4" × 3/8" square notch, 70 ft²/bag | 2 × 50 lb bags |
Tile counts use the covered size — the tile plus one grout joint — because that is the module that actually repeats across the floor. On 12 in tile the joint barely matters; on 2 in mosaic it changes the count by a fifth. Grout is derived rather than looked up in a chart: each tile owns one joint along its length and one along its width, so the volume is thickness × joint width × (length + width) over the module area, at about 100 lb per ft³ for dry sanded grout. That gives 0.125 lb/ft² here. Thinset coverage is the trowel manufacturer's figure and drops fast with notch size — large-format tile needs both a bigger notch and back-buttering. Buy every box from the same dye lot and check the lot number on each one: tile colour varies between runs and a mid-floor change is permanent.
Enter your area and tile size to find how many tiles and boxes you need, plus the grout and thinset — with the joint width and waste factor built in.
How to use this calculator
- Enter the room size or the total area. For an L-shaped room, split it into rectangles and add them.
- Pick your tile size from the presets, or choose Custom and type the dimensions.
- Set the grout joint — 1/16 to 1/8 in for rectified tile, 3/16 to 1/4 in for standard pressed tile.
- Enter tiles per box from the label, and pick the trowel that matches your tile size.
- Set the waste factor: 10% straight, 15% diagonal, 20% for a complicated room or pattern.
The formula
Covered area per tile = (Tile length + Joint) × (Tile width + Joint) · Tiles = Area ÷ Covered area
Grout lb/ft² = 144 × Thickness × Joint × (L + W) ÷ [(L + Joint)(W + Joint)] × (100 ÷ 1728)
Worked example — 200 ft² of 12 × 12 in tile
Standard pressed porcelain, 3/8 in thick, 1/4 in grout joint, 12 tiles per box, 10% waste.
- Covered size: 12.25 × 12.25 in = 150.06 in² = 1.042 ft²
- Tiles, exact: 200 ÷ 1.042 = 191.9 → 192 tiles
- With 10% waste: 220 ÷ 1.042 = 211.1 → 212 tiles
- Boxes: 212 ÷ 12 = 17.7 → 18 boxes
- Grout: 220 × 0.125 = 27.5 lb — three 10 lb bags
- Thinset: 220 ÷ 70 = 3.1 → 4 bags at a 1/4 × 3/8 in notch
Note that 192 tiles cover exactly 200 ft², not 192 ft². The joint is doing real work — over a whole floor it accounts for about eight tiles you do not have to buy.
Why the grout joint changes the count
A 12-inch tile is not 12 inches of floor. With a 1/4-inch joint it occupies 12.25 inches, and that 4% difference is worth eight tiles across a 200 ft² floor. On large tile the effect is small; on small tile it is substantial:
| Tile | Joint | Covered area | Extra vs. tile alone |
|---|---|---|---|
| 24 × 24 in | 1/8 in | 4.042 ft² | +1% |
| 12 × 12 in | 1/4 in | 1.042 ft² | +4% |
| 3 × 6 in subway | 1/8 in | 0.133 ft² | +6% |
| 2 × 2 in mosaic | 1/8 in | 0.031 ft² | +13% |
The same relationship runs the other way for grout: the smaller the tile, the more joint per square foot, and the more grout you need. A mosaic floor can take several times the grout of the same area in 12-inch tile.
Choosing a joint width
The joint is not decorative — it absorbs dimensional variation between tiles and gives the floor somewhere to move. What width you need depends on how precisely your tile was made:
- Rectified tile is machine-cut after firing to a precise size, so it can take a 1/16 to 1/8 inch joint. That is what gives the near-seamless look on large-format installations.
- Standard pressed tile varies slightly from piece to piece as it shrinks in the kiln. It needs 3/16 to 1/4 inch so the joint can absorb the difference — force it tighter and the lippage between tiles becomes obvious.
- Natural stone varies most of all, and hand-made or tumbled stone may need 3/8 inch or more.
Never go below 1/16 inch. Tile and its substrate expand and contract at different rates, and with nowhere to move the floor will tent or the tiles will crack. That is also why perimeter expansion joints exist — leave a gap at every wall, hidden by the baseboard.
Grout, thinset, and the trowel that decides both
Trowel notch size is the input most people guess at, and it drives your thinset quantity directly. The rule is that the notch should be about two-thirds of the tile thickness, and it grows with tile size because larger tile needs a thicker bed to bridge substrate irregularities:
| Trowel notch | Tile size | Coverage per 50 lb bag |
|---|---|---|
| 1/4 × 1/4 in square | Up to 8 in | ≈ 95 ft² |
| 1/4 × 3/8 in square | 8–12 in | ≈ 70 ft² |
| 1/2 × 1/2 in square | 12–16 in | ≈ 45 ft² |
| 3/4 × 3/4 in U-notch | 16 in and up | ≈ 30 ft² |
Large-format tile — anything with a side over 15 inches — also needs back-buttering, a skim of thinset on the back of each tile, to reach the 80–95% coverage the standards require. Budget more thinset than the table suggests when you are doing that.
Buy it all at once
Tile is fired in batches and the colour varies between them. The dye lot number is printed on every box. If you run short and buy more later, there is a real chance the new boxes will not match, and the difference is usually visible across a floor in a way that cannot be fixed without pulling tile.
This is the strongest argument for a genuine waste factor rather than an exact count. It also argues for keeping a box of leftovers: tile gets cracked years later by a dropped pan, and a spare from the original lot makes that a fifteen-minute repair instead of a new floor.
Common mistakes to avoid
- Ignoring the joint. Over-orders on large tile and under-orders nothing — but on mosaic it throws the count out by more than the waste factor.
- Using a 10% waste factor on a diagonal layout. Diagonal needs 15%; every perimeter cut is a 45-degree offcut you cannot use elsewhere.
- Buying tile from mixed dye lots. Check the lot number on every box before leaving the store.
- Guessing the trowel size. Too small and you get hollow spots that crack under load; too large and thinset squeezes up into the joints.
- Skipping perimeter expansion joints. A floor with nowhere to expand will find somewhere.
How we calculate this
Tile counts use the covered size: (tile length + joint) × (tile width + joint), which is the module that repeats across the surface. Waste is applied to the area, and both the exact and waste-adjusted counts are shown. Grout is derived rather than read off a chart, so it holds for any tile size — each tile owns one joint along its length and one along its width, since every joint is shared with a neighbour, giving a grout volume of thickness × joint width × (length + width) over the module area, at about 100 lb per ft³ for dry sanded grout. That yields 0.125 lb/ft² for a 12 × 12 in tile 3/8 in thick with a 1/4 in joint, squarely inside the 0.12–0.15 range the manufacturers' charts publish. Thinset coverage uses the trowel manufacturer's per-bag figures.
Sources
Frequently asked questions
How many 12x12 tiles do I need for 200 square feet?
With a 1/4-inch grout joint, each 12-inch tile actually occupies 12.25 by 12.25 inches — 1.042 square feet. So 200 square feet needs 192 tiles exactly. Add the standard 10% waste factor and you are buying 212 tiles, which is 18 boxes of 12.
How much extra tile should I buy?
10% for a straight layout in a simple rectangular room. 15% for a diagonal layout, because every tile meeting a wall gets cut at 45 degrees and the offcut is unusable. Go to 20% for a room with lots of corners, alcoves, or a herringbone or chevron pattern. Buy it all at once — matching a dye lot later is often impossible.
Does the grout joint change how many tiles I need?
Yes, and much more than people expect on small tile. A 12-inch tile with a 1/4-inch joint covers 4% more area than the tile alone. A 2-inch mosaic with a 1/8-inch joint covers 13% more. This calculator always works from the covered size — tile plus one joint — because that is the module that actually repeats across the floor.
How much grout do I need?
It depends on the tile size, its thickness, and the joint width, so a single number per square foot is meaningless. A 12 by 12 inch tile that is 3/8 inch thick with a 1/4 inch joint needs about 0.125 pounds per square foot — roughly 25 pounds for a 200 square foot floor. A 2-inch mosaic with the same joint needs several times more, because there is vastly more joint per square foot.
How much thinset do I need?
It comes down to trowel size, which comes down to tile size. A 1/4 by 1/4 inch square notch covers about 95 square feet per 50-pound bag and suits tile up to 8 inches. A 1/2 by 1/2 inch notch covers about 45 square feet and is what 12 to 16 inch tile needs. Large format tile also needs back-buttering, which uses more again.
What size grout joint should I use?
1/16 to 1/8 inch for rectified tile, which is machine-cut to a precise size. 3/16 to 1/4 inch for standard pressed tile, which varies slightly and needs the joint to absorb the difference. Never go below 1/16 inch — tile expands and contracts, and with no joint to move into it will tent or crack. Joints wider than 1/8 inch need sanded grout.
Why does dye lot matter when buying tile?
Tile is fired in batches and colour varies noticeably between them, especially in glazed and natural stone products. The lot number is printed on the box. Buying all your tile from one lot means the floor is consistent; topping up later from a different lot often produces a visible patch that cannot be fixed without pulling tile. This is the single strongest reason to add a real waste factor rather than buying exactly what you calculated.
How do I calculate tile for a wall or backsplash?
Exactly the same way — enter the wall area instead of the floor area. For a backsplash, measure from the countertop to the underside of the upper cabinets and multiply by the run length. Subtract nothing for outlets; you cut around them and the offcuts are too small to reuse, so treating them as full coverage is the right call.