For mosaics use the chip size, not the mesh sheet size.
Surface 1
Backsplash is often 18 in = 1.5 ft.
Advanced options
Coverage is set by the notch, not the tile.
From the carton. Leave 0 to skip box counts.
On top of the pattern allowance.
This tile calculator works out how many tiles you need, plus grout and thinset — using the joint-volume method that manufacturer coverage charts are built on, rather than a single guessed figure.
The short answer
Tiles = area × waste ÷ tile area. A 12 × 12 in tile covers exactly 1 ft², so an 80 ft² floor at 10% waste needs 88 tiles.
Grout depends on tile size, not just area. That same floor needs under 6 lb — one 25 lb bag covers 371 ft². The same 80 ft² in 1 × 1 mosaic needs 37 lb, because small tiles have far more joint length per square foot.
On this page
How to use this tile calculator
Pick your tile size and joint width, choose a layout pattern from the header toggle, then enter the surface. Four modes:
- Floor — length and width
- Wall or backsplash — run length and height
- Shower — calculates three walls from the enclosure dimensions
- Known area — you’ve already measured
The results give tile count, grout in bags and thinset in 50 lb bags, with the reasoning shown underneath so you can check it against your product’s own chart.
Under Advanced options: trowel notch (defaults to the TCNA recommendation for your tile size), back-buttering, grout bag size, box coverage and price.
Counting tiles
Tiles = (Area × waste factor) ÷ (Tile L × Tile W ÷ 144)
A 12 × 12 in tile covers 1.00 ft²
18 × 18 covers 2.25 ft² · 24 × 24 covers 4.00 ft²
3 × 6 subway covers 0.125 ft²
| Tile size | Coverage each | Tiles per 100 ft² |
|---|---|---|
| 1 × 1 in mosaic | 0.0069 ft² | 14,400 |
| 2 × 2 in mosaic | 0.0278 ft² | 3,600 |
| 3 × 6 in subway | 0.125 ft² | 800 |
| 4 × 4 in | 0.111 ft² | 900 |
| 12 × 12 in | 1.00 ft² | 100 |
| 6 × 24 in plank | 1.00 ft² | 100 |
| 12 × 24 in | 2.00 ft² | 50 |
| 18 × 18 in | 2.25 ft² | 45 |
| 24 × 24 in | 4.00 ft² | 25 |
Note that a 6 × 24 plank and a 12 × 12 both cover exactly one square foot — but they need very different amounts of grout, which is where the next section comes in.
Grout is about joint length, not area
This is the part almost everyone gets wrong, including several published calculators. Grout quantity has almost nothing to do with how many square feet you’re tiling and almost everything to do with how much joint length sits in each square foot.
Small tiles have vastly more perimeter per unit of area. A square foot of 1 × 1 mosaic contains 144 tiles and hundreds of inches of joint. A square foot of 12 × 12 tile contains one tile and 48 inches of joint. Same area, roughly seven times the grout.
Joint volume = [(L + J)(W + J) − (L × W)] × T
Per ft² = Joint volume × 144 ÷ (L + J)(W + J)
Pounds = Per ft² ÷ 1728 × 105
L, W = tile length and width · J = joint width · T = tile thickness, all inches
105 lb/ft³ is the density of cured cementitious grout
The tile thickness matters because it sets the depth of the joint. A thicker tile means a deeper joint and proportionally more grout — which is why thick porcelain uses more than thin wall tile at the same joint width.
Why published grout figures disagree so wildly
Search for grout coverage and you’ll find claims that a 25 lb bag covers 73 square feet, 98, 240, 365 — all for roughly the same 12 × 12 tile. That’s a five-fold spread, and unlike most estimating disagreements, this one has a clear answer.
The formula above was checked against four independent manufacturer data points. It agrees with all of them:
| Published source | Their figure | Formula | Agreement |
|---|---|---|---|
| Mapei — 12×12, 3 mm joint, 6 mm depth | 0.039 lb/ft² | 0.040 | +3% |
| TEC chart — 12×12×3/8, 1/8 in joint | 0.069 lb/ft² | 0.067 | −2% |
| 1×1 mosaic, 1/8 in — 25 lb covers 54 ft² | 0.463 lb/ft² | 0.459 | −1% |
| Mapei — 2×2 mosaic, 100 ft² ≈ 23 lb | 0.230 lb/ft² | 0.250 | +9% |
A commonly cited claim is 0.34 lb per square foot for 12 × 12 tile at a 3/16 inch joint, giving 73 ft² per 25 lb bag. The geometry gives 0.100 lb/ft², or about 250 ft² per bag — and that matches the manufacturer charts. The 0.34 figure is roughly three and a half times too high, and following it means buying three bags where you need one.
Over-buying grout is a small waste. But the same error appearing on calculator sites is worth knowing about, because it’s the sort of figure people quote back at each other.
Grout by tile size
At a 1/8 inch joint, with typical tile thickness for each size.
| Tile | lb per 100 ft² | 25 lb bag covers |
|---|---|---|
| 1 × 1 in mosaic | 45.9 | 54 ft² |
| 2 × 2 in mosaic | 25.0 | 100 ft² |
| 3 × 6 in subway | 16.3 | 153 ft² |
| 4 × 4 in | 16.3 | 153 ft² |
| 6 × 24 in plank | 8.4 | 299 ft² |
| 12 × 12 in | 6.7 | 371 ft² |
| 12 × 24 in | 5.1 | 494 ft² |
| 18 × 18 in | 4.8 | 520 ft² |
| 24 × 24 in | 3.6 | 691 ft² |
Joint width scales grout almost linearly. For the same 12 × 12 tile:
| Joint width | lb per 100 ft² | 25 lb bag covers | Grout type |
|---|---|---|---|
| 1/16 in | 3.4 | 737 ft² | Unsanded |
| 1/8 in | 6.7 | 371 ft² | Either — the changeover point |
| 3/16 in | 10.0 | 250 ft² | Sanded |
| 1/4 in | 13.3 | 189 ft² | Sanded |
| 3/8 in | 19.6 | 128 ft² | Sanded |
Use unsanded grout below 1/8 inch and sanded at 1/8 inch and above. Sanded grout in a very narrow joint won’t pack properly; unsanded in a wide joint shrinks and cracks. Sand also scratches soft stone and polished glass, so check the product data sheet for those.
Thinset is set by the trowel, not the tile
Thinset coverage is determined by the notch size of your trowel, which sets the mortar bed depth. TCNA publishes trowel recommendations by tile size.
| Tile size | Trowel notch | Per 50 lb bag |
|---|---|---|
| Mosaics up to 2 in | 3/16 in V-notch | ~95 ft² |
| Up to 8 × 8 in | 1/4 × 1/4 in square | ~85 ft² |
| 8 to 15 in | 1/4 × 3/8 in square | ~65 ft² |
| 15 in and larger | 1/2 × 1/2 in square | ~32 ft² |
Note the range: the same 50 lb bag covers 95 ft² of mosaic or 32 ft² of large format. Three times the difference, entirely because of the trowel.
For tiles with any edge over 15 inches, back-buttering — a thin skim coat on the back of the tile — is treated as mandatory by most manufacturers. It fills the factory texture so every trowel ridge makes contact, and it’s the difference between 80% coverage and the 95% that a floor installation should achieve.
It also uses about 18% more thinset. A 1/2 inch trowel dropping from 32 to 26 ft² per bag is a real cost on a large floor, and it’s included automatically for tiles at or above 15 inches.
Waste factors
| Situation | Allowance |
|---|---|
| Straight lay, simple rectangular room | 10% |
| Diagonal 45° | 15% |
| Herringbone | 15% |
| Large format 15 in and above | +5% |
| Rooms with many cuts, niches, curbs | +5% |
Large format gets its own surcharge because an off-cut from a 24 inch tile is usually unusable — there’s rarely another gap that exact size. With a 4 inch tile, most cuts get reused somewhere along the perimeter.
Large format tile
Anything with an edge over 15 inches behaves differently, and three things change:
- The substrate must be genuinely flat. Industry guidance for large format is around 1/8 inch deviation over 10 feet. A long tile bridges any hollow, and the resulting lippage at the edge is very visible.
- Back-buttering is required, along with a large-notch trowel and often a levelling clip system.
- Offset patterns are limited. Most manufacturers cap the offset at one third rather than a half brick bond, because tiles have a slight crown and a 50% offset puts the highest point of one tile against the lowest of the next.
Mosaics
This is the single biggest error in mosaic estimating. A 12 × 12 inch mesh sheet of 1 × 1 mosaic is not a 12 × 12 tile for grout purposes — it contains 144 individual chips and needs about seven times the grout.
Enter the chip dimension. If you enter the sheet size, you’ll order one bag where you need seven.
Mosaics also need a smaller trowel notch, since the mortar has to be shallow enough not to squeeze up between chips. And they’re slower to lay: the mesh backing has to sit flat, and the sheets need aligning so the grid runs continuously across the joins rather than showing a wider seam every 12 inches.
Shade and calibre codes
Every box of tile carries a shade code (sometimes called a batch or lot number) and often a calibre code for dimensional tolerance. Tiles are fired in kilns, and both colour and exact size vary slightly between production runs.
- Buy the whole quantity in one order and check every box carries the same codes before you start.
- Mix from several boxes as you lay, rather than working through one box at a time — this blends any within-lot variation instead of concentrating it in patches.
- Keep spare tiles from the same lot. Matching a discontinued tile later is usually impossible.
Tile estimating mistakes to avoid
- Using mesh sheet size for mosaics. Enter the chip dimension or your grout estimate will be wildly short.
- Assuming grout scales with area. It scales with joint length, so tile size dominates.
- Ignoring tile thickness in grout math. Thickness sets joint depth and scales the volume directly.
- Sanded grout in a 1/16 inch joint. It won’t pack; use unsanded below 1/8 inch.
- Skipping back-buttering on large format. You get partial coverage and hollow spots.
- Mixing shade codes. Check the boxes match before opening them all.
- Buying the exact count. Order 10–15% over and keep the spares.
Frequently asked questions
How many tiles do I need?
Divide your area by the coverage of one tile, then add waste. A 12 × 12 in tile covers exactly 1 ft², so an 80 ft² floor needs 88 tiles at 10% waste. An 18 × 18 tile covers 2.25 ft², so the same floor needs 40.
How much grout do I need?
It depends on tile size, joint width and tile thickness — not just area. At a 1/8 inch joint, 12 × 12 tile uses about 6.7 lb per 100 ft², so a 25 lb bag covers 371 ft². The same area in 1 × 1 mosaic needs 46 lb, because small tiles have far more joint length per square foot.
How much does a 25 lb bag of grout cover?
371 ft² for 12 × 12 tile at a 1/8 inch joint, but only 54 ft² for 1 × 1 mosaic and 250 ft² for the same 12 × 12 at a 3/16 inch joint. Any single figure quoted without the tile size and joint width is meaningless.
Why do grout calculators give such different answers?
Mostly because some ignore tile size or thickness. One widely repeated figure claims 0.34 lb per square foot for 12 × 12 tile at a 3/16 inch joint — the geometry and every manufacturer chart give about 0.10, so that figure is roughly three and a half times too high. Check any calculator against your grout maker’s own coverage chart.
How much thinset do I need?
Coverage is set by trowel notch, not tile size directly. A 50 lb bag covers about 95 ft² with a 3/16 in V-notch, 85 ft² with 1/4 × 1/4 in, 65 ft² with 1/4 × 3/8 in, and only 32 ft² with a 1/2 × 1/2 in trowel for large format.
What trowel size should I use?
Per TCNA guidance: 3/16 in V-notch for mosaics up to 2 in, 1/4 × 1/4 in square for tiles up to 8 in, 1/4 × 3/8 in for 8 to 15 in, and 1/2 × 1/2 in for anything 15 in and larger.
Sanded or unsanded grout?
Unsanded for joints under 1/8 inch — it’s smoother and packs into narrow gaps. Sanded at 1/8 inch and wider, because the aggregate resists shrinkage cracking. Sand can scratch polished stone and glass, so check the data sheet for those materials.
Do I need to back-butter tile?
For any tile with an edge over 15 inches, yes — most manufacturers treat it as mandatory. A thin skim on the tile back fills the factory texture so every trowel ridge makes contact. It uses about 18% more thinset, which the calculator accounts for automatically.
How much extra tile should I buy?
10% for straight lay in a simple room, 15% for diagonal or herringbone, and add 5% for large format or rooms with many cuts. Keep the leftovers — tile shade codes vary between production runs and matching later is often impossible.
How do I calculate mosaic tile?
Use the individual chip size, never the mesh sheet size. A 12 × 12 inch sheet of 1 × 1 mosaic contains 144 chips and needs about seven times the grout of a single 12 × 12 tile. Entering the sheet size is the most common and most expensive mosaic estimating mistake.
What are shade and calibre codes?
Codes printed on every box identifying the production run. Tiles are kiln-fired, so colour and exact dimensions vary slightly between batches. Buy all your tile at once, check the codes match, and mix from several boxes as you lay so any variation blends rather than forming patches.
How much grout for a backsplash?
A typical 12 ft run at 18 inches high is 18 ft². In 3 × 6 subway tile at a 1/8 inch joint that’s about 3 lb of grout — a single 10 lb bag with plenty spare. Small wall areas rarely need more than one bag, but always check against your tile size rather than assuming.
Standards and sources
- TCNA Handbook — trowel size recommendations by tile dimension and mortar coverage requirements
- ANSI A108 — Installation of ceramic tile, including mortar coverage criteria
- Grout output validated against published Mapei and TEC coverage charts at four independent points
- Cured cementitious grout density taken as 105 lb/ft³; actual density varies slightly by product
- Tile thickness values are typical for each size; use your product’s actual thickness where it differs
Related calculators
How this tile calculator works out its numbers
Tile count is area times the waste factor, divided by the coverage of one tile. Waste combines a base rate by pattern with surcharges for large format and any extra you set.
Grout uses the joint-volume method: the area of one tile module including its joints, minus the tile itself, times the tile thickness — giving the joint volume, converted to pounds at 105 lb per cubic foot of cured grout, with 10% added for mixing and cleanup loss. This is the same geometry that manufacturer coverage charts are built from, and its output was checked against four published Mapei and TEC data points, agreeing within 1 to 9%.
Thinset is area divided by the coverage rate for the trowel notch, which defaults to the TCNA recommendation for your tile size. Back-buttering reduces coverage by 18% and applies automatically at 15 inches and above.
Always check against your own product data sheet. Grout density varies between formulations, epoxy grouts are sold by kit rather than weight, and tile thickness differs between manufacturers. This calculator produces quantities, not an installation specification — substrate preparation, movement joints, waterproofing and mortar selection should follow the TCNA Handbook and your tile manufacturer’s instructions.