Tile Calculator: Work Out Exactly How Many Tiles You Need

Running out of tiles halfway through a job is one of the most avoidable frustrations in home improvement. The replacement box may come from a different production batch, with a slightly different shade that shows clearly once laid. Buying far too many, on the other hand, wastes money and leaves heavy boxes to store or return. A tile calculator removes the guesswork by turning your room measurements and tile size into a box count, including a sensible allowance for cuts and breakages. This guide explains the measurements, the wastage rules, and the checks that keep a tiling job on track.

The Tile Calculator takes the length and width of the area, the size of a single tile, and a wastage percentage, and returns the number of tiles and boxes you need. It does the arithmetic reliably, but it cannot measure your room for you, and the quality of its answer depends entirely on the quality of your measurements. Measure twice, write the numbers down, and only then calculate. A calculator used with a guessed measurement gives a confident-sounding wrong answer, which is worse than an honest estimate.

Start by defining the area to be tiled, not the area of the room. A bathroom floor is rarely a perfect rectangle: baths, toilet pedestals, vanity units and door thresholds all remove or complicate parts of it. Sketch the floor on paper, divide it into rectangles, and measure each rectangle separately. For walls, measure each wall's width and height, then subtract large areas that will not be tiled, such as windows and doors, while leaving small cut-outs in the calculation, because cutting around a small pipe or socket consumes tiles rather than saving them. The sketch matters because it forces you to notice the awkward corners where cuts will happen.

Measuring correctly

Use a tape measure, not a guessed stride or a phone estimate, and measure in the same unit throughout, converting at the end if needed. Measure length and width at more than one point, because walls are rarely perfectly straight: a wall that measures 3.02 metres at one end and 2.96 metres at the other should be calculated at the larger figure, or the tiles will run short at the wide end. Note the measurements in centimetres or metres consistently, and double-check any number that looks like a transposition, such as 2.13 written as 2.31. Most tiling errors are measurement errors, not calculation errors.

Tile size needs the same care. Check the actual tile, including whether the stated size is nominal or exact: a tile sold as 30 centimetres may actually measure 29.8 centimetres once grout joints are considered, and some manufacturers state the size including the joint while others do not. If you are unsure, measure one tile with a ruler and use the real figure. Also confirm how many tiles come in a box, because the calculator's box count depends on it, and box quantities vary by product. Buying by tile count alone and then discovering the box size at the shop is a needless second trip.

Grout joints affect the result slightly, because each joint consumes a small amount of area. For large tiles the effect is negligible, but for small mosaic tiles the joints can add up. If your calculator includes a grout width option, use the joint width your tiler plans to use, typically 2 to 5 millimetres for floor tiles. If it does not, a slightly higher wastage allowance covers the difference. Do not obsess over millimetres here; the wastage allowance, discussed next, is deliberately larger than the grout effect, and it is the allowance that protects you.

Wastage: the allowance that saves the job

Wastage covers tiles cut to fit edges, tiles broken during cutting or laying, and tiles kept as spares for future repairs. The right percentage depends on the room's shape and the laying pattern. A plain rectangular room with a straight grid pattern typically needs 5 to 10 percent extra. A room with many corners, angles or obstacles needs 10 to 15 percent, because every obstacle creates offcuts that often cannot be reused. Diagonal patterns and herringbone layouts need 15 to 20 percent, because almost every edge tile is cut at an angle and offcuts rarely fit elsewhere.

It is tempting to set wastage to zero to save money, but that is a false economy. A single broken tile near the end of a job, with no spare from the same batch, can delay completion by days and introduce a shade mismatch that is visible forever. Spares are not waste: keep at least a few full tiles after the job, labelled with the product name and batch number, for future repairs. A chipped tile replaced from the same batch is invisible; one replaced from a later batch may stand out every time you enter the room.

Pattern choice also changes the calculation's meaning. A brick or running-bond pattern staggers joints and uses offcuts more efficiently than a straight grid in some layouts, but it also creates more varied cut sizes. A diagonal pattern looks striking but consumes the most material. Decide the pattern before calculating, because changing it after buying can invalidate the allowance. If your tiler suggests a pattern change mid-job, recalculate before agreeing, especially if the change moves you from a straight grid to a diagonal layout.

Worked example: a bathroom floor

Suppose a bathroom floor measures 2.40 metres by 1.80 metres after accounting for the bath panel, which will not be tiled beneath. The area is 4.32 square metres. The chosen floor tile measures 30 centimetres by 30 centimetres, so each tile covers 0.09 square metres. Dividing gives 48 tiles exactly, before any allowance. The room is fairly rectangular with a toilet pedestal and a door threshold to cut around, so a 10 percent wastage allowance is sensible: 48 multiplied by 1.10 equals 52.8, rounded up to 53 tiles. If tiles are sold ten to a box, that means six boxes, giving 60 tiles, of which seven remain as spares. That spare count is comfortable, not excessive.

Now change one variable: the same floor laid diagonally. At 15 percent wastage, 48 multiplied by 1.15 equals 55.2, rounded up to 56 tiles, still six boxes, but with only four spares. The box count happens to be the same in this example, but in many rooms the diagonal pattern pushes the job into an extra box, and discovering that at the shop is far better than discovering it mid-lay. Also note the rounding rule used throughout: always round up, never down, because a fraction of a tile cannot be bought and the last row of a job is exactly where fractions matter.

A wall example shows why separate measurements matter. A wall 2.40 metres wide and 2.40 metres high, minus a window of 0.60 by 0.90 metres, gives a tiled area of 5.76 minus 0.54, or 5.22 square metres. With 10 by 10 centimetre tiles, each covering 0.01 square metres, the base count is 522 tiles, plus 10 percent wastage gives 575 tiles after rounding up. That large number surprises beginners, but small tiles accumulate quickly, and it is precisely the kind of arithmetic a calculator exists to handle without slips.

Checks before you buy

Before ordering, verify three things. First, that all measurements belong to the same area and unit, and that the sketch matches the room: walk the room with the sketch in hand and confirm each rectangle. Second, that the tile size and box quantity match the product you will actually buy, not a similar product you looked at earlier. Third, that the batch numbers on all boxes match when they arrive, because mixed batches are the most common cause of visible shade differences, and the time to spot them is before laying, not after.

Also plan the layout's starting point. Tilers usually start from a visible centreline or a focal wall so that cut tiles at the edges are balanced rather than leaving a sliver on one side. A row that ends in a sliver less than a quarter tile wide looks poor and breaks easily, so adjusting the starting point by half a tile can transform the result. Discuss this with your tiler before the first tile is fixed, because moving a started layout is costly. The Percentage Calculator is handy for checking wastage arithmetic independently, and the Flooring Material Calculator can help when a project mixes tiled and non-tiled flooring in one room. For a related measuring guide, see Flooring Material Calculator Guide.

FAQs

Should I include the area under the bath or vanity? Only if it will actually be tiled. Areas permanently hidden under a fitted bath or vanity are usually left untiled to save material, but confirm with your tiler, because some prefer a full tiled floor beneath fittings for waterproofing reasons.

What if my room is not rectangular? Divide it into rectangles and triangles, calculate each part, and add the results. For triangular sections, use half the base multiplied by the height. A calculator that accepts total area lets you enter the summed figure directly.

How many spare tiles should I keep? Keep at least five percent of the job or a few full tiles, whichever is larger, stored flat in a dry place with the product and batch details noted on the box. Future repairs will thank you.