Nobody wants to be the person standing at the trade counter mid-project, hoping the batch number on the shelf matches the boxes at home. This tile calculator tells you exactly how many floor tiles to buy by combining your room’s measurements with the size of your chosen tiles, a sensible waste allowance, and your grout joints.
It works for square and rectangular tiles of any size — from tiny mosaics to large-format planks — and automatically adds the extra tiles you need for cuts, breakages, and that spare box every tiler keeps under the stairs. The result gives you a tile count, the number of boxes to buy, and the estimated coverage area so you can price the job properly.
I’m Dave Collins, and I’ve tiled enough floors to know that “eyeballing it” always ends in either a panic run to the shop or a stack of expensive tiles you’ll never use. Whether you’re tackling your first bathroom floor or redoing a kitchen, this calculator gives you a reliable buying list before you spend a penny.
How to Use the Tile Calculator
- Enter your floor dimensions: measure the length and width of the room in feet or metres. For L-shaped or irregular rooms, split the floor into rectangles and calculate each part separately, then add the totals.
- Enter your tile size: input the tile’s length and width (for example 12 × 12 in, 60 × 60 cm, or 8 × 48 in for plank tiles). Use the actual tile face size, not including grout.
- Set your grout joint width: typical floor joints are 2–4 mm (about 1/8 in). Wider joints slightly reduce the tile count — small but worth including.
- Choose your waste allowance: 10% is the standard for square rooms; choose 15% for diagonal layouts, rooms with lots of cuts, or expensive tiles where running short would be painful.
- Enter tiles per box (optional): if you know how many tiles come in a box, the calculator converts your total into boxes to buy — because suppliers sell in whole boxes.
- Read your results: you’ll see the net floor area, the adjusted area with waste, the total tile count, and the number of boxes. Always round up to whole boxes.
How the Calculation Works
The calculator first finds the net floor area (length × width). It then works out the effective area of one tile — the tile’s face area plus its share of the grout joint. Dividing the floor area by the tile area gives the base tile count, which is then increased by your waste percentage and rounded up. If you’ve entered tiles per box, the total is divided by that figure and rounded up to whole boxes.
Worked example: a 10 × 12 ft bathroom floor is 120 sq ft. With 12 × 12 in tiles (1 sq ft each) and a 10% waste allowance: 120 × 1.10 = 132 tiles. If tiles come 10 to a box: 132 ÷ 10 = 13.2, which rounds up to 14 boxes. For 24 × 24 in (2 × 2 ft, 4 sq ft) tiles on the same floor: 120 ÷ 4 = 30 tiles, plus 10% = 33 tiles — so you’d order 4 boxes of 10, giving you a few spares.
This is an estimate, not a cutting plan. Very small rooms, diagonal patterns, and herringbone layouts generate more offcuts — treat 15% as the floor (no pun intended) for anything patterned, and don’t expect the maths to cover a bad batch of tiles with lots of chips.
Tips for Accurate Results
- Measure wall to wall: measure the floor itself, not the rug — tiles run under skirting, so go right into the corners. In the UK, remember tiled areas often run under the bath or vanity plinth.
- Use diagonal waste for angled layouts: diagonal and herringbone patterns need 15% waste at minimum; every angled cut produces an unusable offcut, and it adds up fast.
- Check the tile’s actual size: a “12 inch” tile is often 11.75 in. Check the box for the nominal vs. actual size — over a big floor, a quarter inch per tile shifts the count.
- Keep a spare box: tiles get discontinued and dye batches change. One extra box (already covered by your waste allowance) stored in the loft is cheap insurance against future damage.
- Order everything at once: batch and shade numbers vary between production runs. Ordering all boxes together from the same batch avoids subtle tone differences across the floor.
- Don’t forget grout and adhesive: the calculator covers tiles only. Budget roughly one 20 kg bag of adhesive per 4–5 m² (about 40–50 sq ft) for floor tiles, and check your grout’s coverage per bag.
Frequently Asked Questions
How many tiles do I need for a 10×10 bathroom floor?
A 10 × 10 ft floor is 100 sq ft. With standard 12 × 12 in tiles and 10% waste, that’s about 110 tiles — 11 boxes of 10. With larger 24 × 24 in tiles you’d need roughly 28 tiles including waste.
What waste percentage should I use?
Use 10% for straightforward square layouts in rectangular rooms. Step up to 15% for diagonal patterns, herringbone, rooms with many corners or doorways, and any tile that’s expensive or hard to reorder.
Does the calculator include grout joints?
Yes — when you enter your grout joint width, the calculator adds it to each tile’s effective footprint, which slightly reduces the tile count. For most floor jobs the difference is small, but it keeps the count honest.
Should I tile under appliances and vanities?
Generally yes for freestanding vanities and appliances that may move; it avoids an awkward un-tiled strip if you rearrange. For built-in units that will never move, tiling up to them is fine — just remember the calculator counts the full floor area you enter, so measure accordingly.
How do I lay the tiles once I’ve bought them?
Start with a dry layout from the centre of the room to balance the cuts at the edges — our beginner’s guide to laying floor tiles walks through the whole process. For a deeper dive into the numbers, see how to calculate floor tiles needed for worked examples of trickier room shapes.