Working out how many tiles you need before you head to the builders merchant can save you time, money and the frustration of running short mid-job. This guide walks you through everything you need to know — from calculating your area to choosing the right wastage allowance.
Or skip straight to our free Tile Calculator and get an instant result.
The Basic Formula
The core calculation is straightforward:
Number of tiles = Room area ÷ Tile area
For example, a room that is 4m × 3m = 12 m². A 600×600mm tile covers 0.36 m². So 12 ÷ 0.36 = 34 tiles before wastage. Add 10% (4 tiles) and you need to buy 38 tiles.
Step 1 — Measure Your Room
Measure the length and width of the room in metres. For irregular rooms, break the area into rectangles and add them together. Measure twice — getting this wrong is the most common cause of buying too few tiles.
For rooms with obstacles such as a bath or island unit, it is generally easier to calculate the full floor area and deduct the obstacle area afterwards, rather than trying to measure around it.
Step 2 — Know Your Tile Size
Tile sizes are given as length × width in millimetres. The most common sizes in UK homes are:
- 600 × 600 mm — popular for open-plan floors and large bathrooms
- 600 × 300 mm — versatile, works on floors and walls
- 300 × 300 mm — traditional choice for smaller rooms and walls
- 1200 × 600 mm — large format, increasingly popular in kitchens
Step 3 — Add a Wastage Allowance
Always buy more tiles than the bare calculation suggests. Wastage comes from cuts at edges, breakages during cutting and fitting, and spare tiles kept for future repairs. As a rule of thumb:
- 10% for a straightforward rectangular room with a straight lay pattern
- 15% for a room with alcoves, door recesses or fitted furniture
- 20% or more for a diagonal (45°) lay pattern, which produces far more edge cuts
One critical tip: always buy all your tiles from the same batch number. Tile colour varies slightly between production batches (the dye lot). Even tiles from the same range can look noticeably different side by side if they come from different batches. Check the batch number printed on the box before you buy.
Step 4 — Account for the Grout Joint
Tiles are not laid edge to edge — there is a small gap between them filled with grout. This grout joint typically ranges from 2mm for rectified tiles (precisely cut to a consistent size) up to 5mm for non-rectified tiles. Our tile calculator includes the grout joint in the calculation by default, set at 3mm.
Including the grout joint slightly reduces the number of tiles needed because each tile effectively covers a slightly larger footprint.
How Many Boxes Do I Need?
Once you have your total tile count, divide by the number of tiles per box and round up to the nearest whole box. The tiles-per-box figure is on the box label and usually also on the retailer website. Our Tile Calculator has an optional box count field that does this automatically.
Quick Reference — Tiles per m²
| Tile Size | Tiles per m² (3mm joint) |
|---|---|
| 300 × 300 mm | 10.7 |
| 450 × 450 mm | 4.8 |
| 600 × 300 mm | 5.5 |
| 600 × 600 mm | 2.7 |
| 800 × 400 mm | 3.1 |
| 1200 × 600 mm | 1.4 |
Use our free Tile Calculator to get an accurate count for any room size and tile size combination, including your exact grout joint and wastage percentage.
