Tiling looks simple until you stand in the shop trying to buy the right number of boxes. Buy too few and the job stops halfway, and a second order may arrive in a different shade, which shows clearly on a finished floor. Buy too many and you have paid for boxes that sit in the garage for years. This estimator removes the guesswork. Enter the size of the floor or wall, the size of one tile, a waste allowance, and how many tiles come in a box, and it returns the tiles and boxes to buy.
The maths is straightforward. First the tool multiplies length by width to get the area in square metres. Then it works out the area of one tile: a 30 cm by 30 cm tile covers 0.09 square metres, so one square metre needs about 11.1 tiles. Dividing the room area by the tile area gives the exact tile count with no waste at all, which no real job ever achieves. That is why the waste allowance matters so much, and why it is an input you control rather than a hidden number.
Here is a worked example. A room 5 metres by 4 metres covers 20 square metres. With 30 cm square tiles, the exact count is about 222 tiles. Adding the default 10 percent waste gives about 244 tiles, rounded up to 245. At 10 tiles per box, that is 25 boxes, because 24 boxes hold only 240 tiles. That final rounding up at the box step is where many estimates fail: buying 24 boxes leaves you five tiles short, and five tiles short means an unfinished corner.
Choosing the waste percentage is the main judgement call. Use 10 percent for a square or rectangular room with a straight layout, where cuts happen only at the edges. Use 15 percent for diagonal layouts, rooms with many corners, doorways, or fixed obstacles such as baths and kitchen units, because every angle creates an offcut. Large tiles break more often during cutting, so lean higher with big formats. Small mosaic sheets waste less, but they still need spares for future repairs.
Measure carefully before you trust any number. Measure the length and width at the widest points, and for walls measure each wall separately and add the areas together. Subtract large areas that will not be tiled, such as a big window or a built-in cupboard, but do not subtract small fittings like sockets and taps, because the waste allowance already covers them. Measure the tile itself, not the box label alone, since nominal sizes can differ slightly from real sizes.
Boxes are sold by the box, never by the single tile, so the box count is the number that matters at the checkout. Keep at least a few spare tiles after the job, ideally a full box if you have storage space. Tiles get discontinued, and a cracked tile in five years is a small repair if you kept spares and a full re-tile if you did not. Store spares flat, dry, and labelled with the tile name and batch number.
Remember that this is a planning estimate, not a professional quote. It does not allow for patterned layouts that need matching, for borders and trims, or for uneven walls that need levelling first. If your room has an unusual shape, split it into rectangles, estimate each one, and add the results. For a large or expensive job, show your numbers to the tile seller and ask them to check the box count before you pay. Ask the seller to confirm the tile shade and batch too, so every box you buy matches.