How to measure an area for tiling
Measure the length and width of the area at floor or wall level, in metres, to the nearest ten millimetres where you can. Most rooms are not perfectly square, so it pays to measure at more than one point along each wall and use the largest figure, since a tiler needs to cover the full space, not the average of it. If the area is an awkward shape, an L-shaped bathroom floor or a kitchen with a bench overhang, break it into simple rectangles on paper, work out each one's area, and add the totals together before entering a single combined figure here. Doing that by hand for two or three rectangles takes a few minutes and is far more reliable than trying to estimate an irregular shape as one number.
Tile size matters just as much as area, because it decides how many individual tiles that area breaks into. Tile dimensions are almost always quoted in millimetres on the box, not metres, so this calculator takes the length and width in millimetres and converts them for you. A common size like 600 by 300 millimetres, or a large-format 600 by 600, will need noticeably fewer tiles across a given area than a smaller mosaic or subway tile, even though the square metre coverage is the same either way.
What a tiler means by set-out
Set-out is the planning step a tiler does before cutting a single tile: working out where the first full tile goes, which direction the pattern runs, and how the cuts fall at the edges of the room. A good set-out puts full tiles in the most visible spots, the doorway, the middle of the floor as you walk in, and pushes the narrow cut pieces to the edges near skirting boards or under cabinetry where they are far less noticeable. A poor set-out does the opposite, leaving an awkward sliver of tile right in the doorway because nobody planned the starting point.
Set-out affects how much wastage a job actually generates, which is exactly what the wastage percentage in this calculator is standing in for. A straightforward grid layout, tiles running parallel to the walls in a simple room, typically produces less offcut waste because most cuts are simple straight lines and the offcuts from one edge can sometimes be reused on the opposite wall. A layout with a lot of edges, alcoves, or fixtures to tile around will waste more, because more of the cuts are small, irregular, and unusable elsewhere.
Why a diagonal or herringbone layout wastes far more
A tile laid on the diagonal, at 45 degrees to the walls, looks sharp in the right room, but it comes at a real cost in material. Every edge of the room now meets the grid at an angle instead of square on, so almost every border tile needs a diagonal cut, and the triangular offcuts left over are usually too small and the wrong shape to reuse anywhere else in the room. Herringbone is even more demanding again, since it is built from individual rectangular pieces set at alternating angles, with cuts needed at every row along each wall, not just around the room's outer edge.
If you are planning a diagonal or herringbone layout, set your wastage percentage noticeably higher than you would for a straight lay. A straightforward grid on a simple rectangular room might only need a modest allowance. A diagonal layout, or a room with a lot of corners and fixtures, can easily need double that or more. There is no single correct figure here because every room and every pattern is different, which is exactly why this calculator asks you to set the wastage yourself rather than assuming one number fits every job. If you are unsure, a tiler who has quoted the job or the supplier who is selling you the tiles will usually have a feel for what a similar layout in a similar room actually used.
Boxes, and why the count on the box matters
Tiles are sold by the box, and the number of tiles in a box varies by size, brand and supplier, not by any fixed rule. A box of large-format 600 by 600 millimetre tiles might hold far fewer pieces than a box of smaller mosaic tiles, simply because more small tiles fit in the same weight or volume of packaging. This calculator asks for the tiles-per-box figure because there is no way to know it in advance. Check the actual box you are buying, or ask the supplier, rather than assuming a round number.
Once the calculator knows how many individual tiles the wastage-adjusted area needs, it rounds that figure up to a whole number of boxes, because a supplier will not sell you nine tenths of a box. That rounding is worth keeping in mind when you compare quotes or plan a budget: the tile count itself might land close to a box boundary, and rounding up one extra box either way can shift the total more than a small change in the wastage percentage would.
Keeping spare tiles from the same batch
Tile colour and pattern are printed or fired in production batches, and even the same product code from the same manufacturer can show a subtle shift in shade or pattern from one batch to the next. This matters far more with tiles than with most other building materials, because a tile floor or splashback is a large, flat, continuously visible surface where a slight colour mismatch between two batches is much easier to spot than it would be on, say, a painted wall.
Buy a few extra tiles from the same batch as the job and keep them somewhere safe, rather than assuming you can go back to the supplier in a year or two and get an exact match. Ranges get discontinued, batches sell out, and even an identical product code from a new production run is not guaranteed to look the same as the batch that is currently on your floor. A handful of spare tiles, stored flat somewhere dry, is cheap insurance against a future repair job that would otherwise mean either an obvious patch of mismatched tile or, worse, retiling an entire area to fix a few cracked pieces near the edge.
Wastage is not the same thing as a mistake
It is worth separating two things that get lumped together as "wastage" in casual conversation but are actually different problems. Cutting waste is the offcut left over whenever a tile has to be trimmed to fit a border, a pipe, or a fixture, and it is unavoidable on any real room, because very few rooms happen to be an exact multiple of the tile size in both directions. Breakage is different: tiles that crack or chip during handling, cutting, or laying, which happens at some rate no matter how careful the installer is, particularly with larger-format or more brittle tile products.
Both are usually rolled into the one wastage percentage for simplicity, and that is a reasonable approach for planning a purchase. But if a job is going badly and you are running short, it is worth knowing which one is actually eating your supply. A run of cutting waste on a fiddly layout is a set-out problem, and a different starting point or pattern might reduce it on the next room. A run of breakages might point to a blade that needs replacing, a batch of tile that is more brittle than usual, or a technique issue worth slowing down for, rather than something a bigger wastage allowance alone will fix.
Grout lines and why they barely change the numbers
Every tile is laid with a small gap around it for grout, usually somewhere between one and a few millimetres depending on the tile and the look you want. It is fair to ask whether that gap should be added to the tile's stated size before working out how many tiles fit an area. In practice, for almost every domestic job, the answer is no, or at least not in a way that meaningfully changes the outcome. The gap is small enough relative to a typical tile size that its effect on the total tile count gets absorbed comfortably inside a sensible wastage allowance.
Where it does start to matter is a mosaic or very small format tile, where the grout gap is a much larger share of each individual tile's footprint, or a job using an unusually wide grout line as a deliberate design choice. In either of those cases, treat the tile size you enter here as the tile plus half its grout gap on each side, which will push the tile count down slightly and better reflect what actually fits. For a standard-format tile with a standard grout width, though, this is not worth the extra arithmetic, and the wastage allowance already covers the gap comfortably.
Where this fits with the rest of the job
Once you know how many tiles and boxes a job needs, the next cost to work out is usually labour, adhesive, grout and any trims or edging, none of which this calculator covers, because tiling labour rates and adhesive coverage vary too much by job to guess at here. If you are pricing a tiling job for a customer, our markup and margin calculator turns a materials total like the one this page gives you into an actual sell price, once you have added labour and everything else the job needs. And if you run a tiling business and your own site is not bringing in the enquiries it should, our tilers page covers what actually needs to be on a tiler's site, beyond a gallery of finished bathrooms.