Tile Calculator
How many tiles and how many boxes a floor or a wall takes — with the grout joint counted, which is the part almost every other tile calculator throws away. Waste stays on its own line so you can argue with it.
The surface, the tile, and the joint
An L-shaped room splits into rectangles: add their square footage and enter the total here.
The long side of the floor, or the run of the wall.
The short side, or the height of the wall being tiled.
The nominal face size printed on the box — 12, 18, 24, or 6 for subway tile.
Same as the length for a square tile. A 3 × 6 subway tile is 6 long and 3 wide.
0.0625 for 1/16, 0.125 for 1/8, 0.1875 for 3/16, 0.25 for 1/4. It is in the arithmetic here, not thrown away — that is why the tile count comes out below naive division.
Ten percent for a straight lay, fifteen for a diagonal, twenty for a herringbone. Kept as its own line below, and set for you by the layout buttons in advanced options.
From the carton label. If the box quotes square feet instead, switch it in advanced options below.
120.00 sq ft takes 118 tiles at 12.125 × 12.125 in a tile, plus a 10% allowance of 12 — which is 13 boxes.
- Net area
- 120.00 sq ft
- Tiles for the area
- 118
- Waste allowance (10%)
- 12 tiles
- Tiles to buy
- 130
- Boxes to buy
- 13
- Spare tiles in the last box
- 0
- Coverage per tile, joint included
- 1.0209 sq ft
- Grout joint to fill
- 236.30 linear ft
- Grout share of the surface
- 2.0512%
- If the joint were ignored
- 132 tiles
- Thinset bags needed
- 2
- Thinset coverage used
- 64 sq ft/bag
| Layout | Allowance | Tiles | Boxes |
|---|---|---|---|
| Straight | 10% | 130 | 13 |
| Diagonal | 15% | 136 | 14 |
| Herringbone | 20% | 142 | 15 |
- Buy one box more than this and keep it sealed. Dye lots differ between production runs, so a replacement box bought later will not match, and a tile discontinued in the meantime cannot be matched at all. A cracked tile in five years is either a spare from the shelf or a floor you re-do.
- The joint is in the count: each tile occupies 12.125 × 12.125 inches of surface, not 12 × 12. A calculator that skips this would have asked for 132.
- Grout is given as linear feet of joint rather than pounds, because pounds need the joint depth — your tile thickness — and coverage varies far more between grout formulations than the geometry does. Take this figure to the bag’s own coverage table.
- Thinset and material cost are both optional: leave the advanced prices at zero to skip the estimate, and pick the trowel notch that matches this tile size — too small a notch under a large tile leaves it unsupported, and too large a notch under a small tile wastes mortar.
Count the module, not the tile
A tiled surface is a grid, and the thing that repeats across it is not the tile. It is the tile plus one joint — the module — because every tile carries half a joint on each of its four sides, which is one whole joint in each direction. Divide the area by the bare tile and you have quietly assumed the grout takes up no room at all.
module = (L + J) × (W + J) • N = ⌈A × 144 ÷ module⌉ • boxes = ⌈(N + waste) ÷ per box⌉- L, W
- The nominal face length and width of one tile, in inches
- J
- The grout joint width in inches — 0.0625 for 1/16, 0.125 for 1/8, 0.25 for 1/4
- A × 144
- The surface in square inches, so it can be divided by a module measured in inches
- ⌈ ⌉
- Rounded up, at every step. Half a tile is a cut, not a purchase, and half a box is not for sale
Grout follows from the same geometry. The joint’s share of the surface is the module area minus the tile area, over the module area; multiply the surface by that share and divide by the joint width and you have the total run of joint in inches. The calculator reports it in linear feet, and stops there: turning linear feet into pounds needs the joint depth — your tile thickness — and a coverage figure that belongs to a specific bag of a specific product.
Two more figures follow from the same numbers. A box priced by coverage rather than piece count converts the way a reader would by hand: the printed square footage divided by the bare tile face, then through the same ceiling as a counted box. Thinset is priced separately, in 50 lb bags, at a coverage set by the trowel notch — a wider tile needs a deeper notch, and a deeper notch lays down more mortar per square foot, so coverage falls as notch size rises. The published figures come from one manufacturer’s technical data sheet, cited below; bag count is the net floor area over that coverage, not the tile count with its waste allowance, because mortar spreads across the substrate rather than across the pieces eventually cut from it.
Laying planks rather than tile? The arithmetic is not the same shape at all, and the flooring calculator is the one you want: no joint width, coverage per carton instead of pieces per box, and a waste allowance that pays for offcuts rather than cuts.
A 10 × 12 floor in 12 inch tile, ⅛ inch joints
The floor is 120 square feet, or 17,280 square inches. Each tile occupies 12.125 × 12.125 = 147.02 square inches once its joint is counted, so the floor takes 17,280 ÷ 147.02 = 117.54, rounded up to 118 tiles. A ten percent allowance is 11.8, rounded up to 12 tiles, giving 130 tiles to buy. At ten tiles a carton that is 13 boxes exactly — and therefore not one spare tile in the house.
Run the same floor the way most calculators do, dividing by the bare 144 square inches of tile, and you get 120 tiles plus a 12-tile allowance: 132. Two tiles of difference on a small job, and the error is systematic — it never goes the other way. Put a 1 inch mosaic on the same floor at the same joint and the gap widens dramatically: the module is 1.125 inches square, 21% of the finished surface is grout, and naive division over-orders by roughly a fifth.
The grout side of the same job: 2.05% of 17,280 square inches is 354 square inches of joint, which at ⅛ inch wide is 2,836 inches — about 236 linear feet of joint to fill. Take that and the joint width to the coverage table on whichever grout you buy.
The advanced options carry the same floor one step further. A 12 inch floor tile is usually set in a 1/4 × 3/8 inch notch, worth about 64 square feet from a 50 lb bag on the manufacturer’s own chart, so 120 ÷ 64 = 1.875, rounded up to 2 bags of thinset. Price a box of tile at $18 and a bag of thinset at $22, and the two together — 13 × $18 plus 2 × $22 — come to $278 in material, tile and thinset only.
One more number that is not in the arithmetic. Thirteen boxes leaves zero spares, so buy a fourteenth and do not open it. See below for why that box is the most valuable thing on this page.
Keep one full box sealed. Dye lots do not come back.
Tile is fired in batches, and no two batches are quite the same colour. That is why boxes carry a dye lot or shade code, and why tile setters check that every carton on a job shares one. The practical consequence is simple and expensive: a box bought later will not match the floor you laid today, even if the product name, the shop, and the size are identical.
And that assumes the tile still exists. Ranges are discontinued constantly — a line that was current when you tiled the kitchen is often gone in three years, and then there is no match at any price. The failure mode is not an abstract one. A dropped pan cracks a tile, and the choice becomes an obviously different patch in the middle of the floor, or lifting and replacing the lot.
One sealed box is a few tens of dollars against that. Write the room on the outside, store it flat and dry, and tell whoever lives there next where it is. It is the cheapest insurance in the whole job, and it is not a waste allowance — the allowance covers the cuts you make on the day, and it will be gone by the evening.
Ten, fifteen, or twenty percent
Ten percent for a straight lay in a room whose walls are square to each other. The cuts are all at the perimeter and most of the offcut from one wall is usable on the next.
Fifteen percent for a diagonal. Every perimeter tile becomes a mitre, the piece left over is a triangle, and triangles are much harder to use again than rectangles.
Twenty percent for a herringbone, where every piece in the field is mitred rather than only the ones at the wall, or for a room with many cuts or an irregular outline — alcoves, a niche, a curved edge, a bathroom dense with fixtures. What drives waste is not floor area, it is the length of edge (or angled cut) per square foot, and a small complicated room has a great deal of it.
The result panel prices all three layouts against your own room, in tiles and in boxes, and the advanced options set the waste field to any of them directly — because a percentage argued about in the abstract is a percentage nobody ever changes. Seeing that herringbone means two more boxes is what makes the choice concrete.
What this calculator assumes
- Tiles are laid on a regular grid, one joint wide in both directions, with the same joint everywhere. A running-bond or offset layout uses the same module and therefore the same count; only its cuts differ, which is what the allowance is for.
- The tile dimensions you enter are the nominal face size printed on the box. Actual fired sizes vary slightly, and rectified tile is trimmed to a tighter tolerance than pressed tile — which is why rectified tile can take a narrower joint, not why it needs a different formula.
- The area is net. Nothing is deducted automatically: subtract a shower pan, a hearth, or an island footprint yourself before you enter a square footage.
- Counts are rounded up at every step — tiles first, then boxes. Rounding to the nearest whole box would leave you short on the last row, and the last row is the one you cannot postpone.
- Grout is reported as linear feet of joint and as a share of the surface, never as pounds. Pounds need the joint depth and a product-specific coverage figure, and a generic estimate would be wrong in both directions depending on the grout.
- Nothing here covers backer board, waterproofing membrane, trim and bullnose pieces, spacers, or the setting-out itself. Where the first tile lands decides how the cuts fall, and no calculator can make that decision for a room it cannot see.
- A box priced by coverage rather than piece count is converted using the bare tile face, not the module with its grout allowance — the same convention the carton label itself uses, since a manufacturer has no way to know this job’s joint width.
- The published trowel-notch coverage figures are typical figures from one manufacturer’s technical data sheet. Every thinset chart moves a little with the product and the substrate, so check the bag before ordering more than a bag or two on the strength of them.
- The material cost estimate covers tile and thinset only, at whatever prices are entered. It does not include grout, labour, backer board, trim, spacers, delivery, or tax.
Tile calculator FAQ
Does the grout joint really change how many tiles I need?
Yes, and always in the same direction. The unit that repeats across a floor is not the tile, it is the tile plus one joint — the module. A 12 inch tile set with a ⅛ inch joint occupies 12.125 inches of run, so a 12 foot wall takes 144 ÷ 12.125 = 11.88 modules, not the 12 that dividing by the bare tile suggests. Across a 10 × 12 foot floor that is 118 tiles rather than 120. Two percent sounds trivial, but it only ever over-orders, it compounds with the waste allowance sitting on top of it, and on mosaic or small-format tile — where the joint is a big fraction of the piece — it is far larger than two percent. A 1 inch mosaic at a ⅛ inch joint is 21% grout by area.
How much extra tile should I buy?
Ten percent for a straight lay in a square room. Fifteen for a diagonal, because every perimeter tile becomes a mitre and the offcut is rarely reusable. Twenty for a herringbone, where every piece is a mitre rather than only the ones at the wall, or for a room with alcoves, niches, a curved edge, or many small cuts — a bathroom floor around a toilet flange and a vanity gets through tile faster than its square footage predicts. Those are allowances for cuts and breakage, not for the future. The spare box is a separate decision, and a more important one. The calculator's advanced options set the waste field to any of the three with one click.
Why does herringbone need more tile than a plain diagonal?
Because every piece is cut at an angle, not just the ones at the perimeter. A diagonal lay only mitres the tiles that meet a wall — the field tiles in the middle are cut once, the same way a straight lay's field tiles are not cut at all. Herringbone mitres every single piece to build the zig-zag, so the whole floor behaves like a diagonal lay's perimeter. Twenty percent, against fifteen for a plain diagonal, is the usual allowance for the difference.
Why should I keep a whole spare box of tile?
Because tile is fired in batches and the colour of a batch is not exactly the colour of the next one. Boxes carry a dye lot or shade code for exactly this reason, and a box bought a year later — even of the same product, from the same shop — will usually be a visibly different lot. If the line has been discontinued in the meantime, and tile lines are discontinued constantly, there is no match at any price. One sealed box costs a few tens of dollars now. Replacing a cracked tile without it means either an obvious patch or pulling up the floor. Buy the spare box, write the room on it, and put it somewhere dry and flat.
How do I work out tile for a bathroom with a shower, a toilet, and a vanity?
Take the room as a rectangle, subtract the footprint of anything that will not be tiled under — a vanity cabinet, a shower pan, a built-in tub — and enter the remainder as a square footage. Do not subtract the toilet: the flange sits on tile, and the cut around it wastes most of that tile anyway. Then push the waste allowance to 20%. Bathrooms are the worst rooms for cuts per square foot, because the fixtures are dense and the room is small, so the perimeter-to-area ratio is high.
How much grout will I need?
This calculator gives you the geometry: the total run of joint in linear feet, and the share of the finished surface that is grout rather than tile. It stops there deliberately. Turning that into pounds needs the joint depth, which is your tile thickness, and then a coverage figure that varies substantially between sanded and unsanded grout, between cement-based and epoxy, and between manufacturers. Take the linear feet and the joint width to the coverage table printed on the bag you are actually buying — that number is specific to that product, and a generic pounds-per-square-foot estimate is not.
How much thinset mortar do I need?
That depends on the trowel notch, and the notch depends on the tile. A small tile set in a shallow 1/4 × 1/4 inch notch might get about 95 square feet from a 50 lb bag; a large-format tile set in a deep 3/4 inch notch might get barely a third of that, because the deeper ridges lay down far more material. The advanced options list four published notch sizes — pick the one that matches this tile, or enter your own bag's printed coverage — and the bag count comes off the net floor area rather than the tile order, because mortar is spread across the substrate, not across the pieces eventually cut from it. Buy one extra bag regardless: running short mid-spread is a worse day than a mostly full leftover bag.
How many 12 × 12 tiles are in a box?
There is no standard, which is why this calculator asks. Cartons of 12 inch porcelain commonly hold anywhere from 8 to 16 pieces, and the label usually quotes square feet of coverage rather than a count. If yours does, the advanced options can take that figure directly: switch "How is the box labeled?" to coverage, enter the square footage from the carton, and the box count updates without any hand division. That conversion uses the bare tile area, since manufacturers quote coverage without joints — not the per-tile coverage shown in the result, which already includes each tile's share of the joint.
Does the calculator price the whole job?
No, and it says so on purpose. The advanced options roll up two costs — tile (boxes × a price per box) and thinset (bags × a price per bag) — because those are the two quantities the geometry above already produces exactly. Grout is deliberately left out of the rollup: it is reported in linear feet, not bags, for the reasons above, and pricing a figure with no weight behind it would invent a precision the geometry does not have. Labour, backer board, trim, spacers, and delivery are not modelled at all. Leave a price field at zero and that half of the estimate disappears rather than showing a wrong number.
Is a tile calculator the same as a flooring calculator?
No, and using one for the other will cost you. Tile repeats on a rigid grid, so its joint width belongs in the count and the answer is a number of pieces. Laminate, vinyl plank and hardwood are cut to whatever length each row needs, are sold by coverage rather than by piece, and put their waste into the offcuts a staggered end-joint pattern leaves behind. If you are laying planks, use the flooring calculator instead — the arithmetic is genuinely different.
Sources and review notes
- Tile Council of North America — publisher of the TCNA Handbook and secretariat for the ANSI A108 and A118 installation standards, the reference North American tile setting is specified against
- NIST Special Publication 811 — the definitions behind the unit conversions used here: 12 inches to the foot, 144 square inches to the square foot
- CUSTOM Building Products — VersaBond Professional Tile Mortar technical data sheet, the source for the trowel-notch coverage figures in the advanced options
The geometry on this page is exact and has nothing behind it that can go stale. The judgement calls are the waste allowances and the thinset coverage figures, all of which are conventional trade figures rather than published standards, and the dye-lot advice, which is a property of how tile is manufactured rather than a rule anybody enforces. Check the carton and the mortar bag: the shade code, the coverage, and the piece count are all printed on them, and all of it varies by product.