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How Many Tiles Do You Need?
Working out how many tiles you need is a straightforward calculation, but getting it wrong is an expensive mistake. Buy too few and you risk not being able to match the same batch later; buy too many and you are wasting money. This calculator handles the maths, but it helps to understand what is going on under the hood.
The basic process: measure the total area to be tiled in square metres, divide by the area of one tile (including grout joints), then add your wastage allowance and round up. For walls, measure height × width of each section. Subtract any large cut-outs such as windows. For floors, measure the room’s length × width.
Always buy a little extra. Tiles from different production runs (batches or shade lots) can vary slightly in colour and texture, even when they appear identical in store. Keeping a few spares means you can replace cracked or damaged tiles years later with a perfect match.
Understanding Tile Sizes
The UK tile market has seen a steady shift towards larger format tiles over the past decade. Large tiles make a room feel bigger, have fewer grout lines to clean, and suit the clean-lined contemporary aesthetic that dominates UK interior design. Here is a guide to the most common sizes and their typical uses:
| Tile Size | Coverage per Tile | Tiles per m² | Common Use |
|---|---|---|---|
| 600 × 600 mm | 0.36 m² | ~2.8 | Large floor areas, open-plan kitchens |
| 300 × 600 mm | 0.18 m² | ~5.6 | Bathroom walls, shower enclosures |
| 300 × 300 mm | 0.09 m² | ~11.1 | Bathroom floors, utility rooms |
| 200 × 600 mm | 0.12 m² | ~8.3 | Subway-style walls, feature tiles |
| 200 × 200 mm | 0.04 m² | ~25 | Traditional kitchens, splashbacks |
| 100 × 100 mm | 0.01 m² | ~100 | Mosaic floors, shower trays |
Note that these are nominal sizes — actual tile dimensions may be slightly smaller, with the grout joint making up the difference. Always confirm the actual dimensions on the product specification before calculating.
Wastage: How Much Extra to Buy?
Wastage occurs because tiles at the edges of a room need to be cut to fit. Some pieces of cut tile are too small to use and are discarded. The more complex your room layout and the smaller your tiles, the higher your wastage percentage. Here is a practical guide:
- 5% wastage: Simple rectangular rooms with no obstacles, straight (grid) laying pattern. Suitable for a perfectly square room with no cuts around sockets or bath panels.
- 10% wastage (recommended default): Standard room with typical cuts around doors, skirting boards, bath edges, or toilet pedestals. A safe choice for most projects.
- 15% wastage: L-shaped rooms, rooms with multiple alcoves, areas with many penetrations (pipes, sockets), or first-time DIYers expecting more breakage.
- 20% wastage: Diagonal (45-degree) or herringbone laying patterns. Diagonal patterns require significantly more cuts at every edge, substantially increasing waste.
For trade or experienced professionals, 10% is a reliable standard. If in doubt, round up to the next box and keep receipts — many tile suppliers accept returns of unopened boxes.
Grout Joints: Why They Matter
The grout joint is the gap left between tiles, filled with grout after laying. It serves both a functional and aesthetic purpose. Functionally, it allows for slight variations in tile size (all tiles have a manufacturing tolerance) and accommodates minor movement in the substrate without cracking tiles. Aesthetically, it defines the look of the finished surface.
The recommended joint width depends on the tile type and size:
- 2–3 mm: Large format porcelain tiles with very consistent dimensions. Creates a near-seamless look.
- 3–5 mm: Standard ceramic and porcelain tiles. The most common choice for UK floors and walls.
- 5–10 mm: Rustic or handmade tiles with irregular edges. The wider joint accommodates natural size variation.
- 10–20 mm: Brick-pattern or very large handmade tiles, or for a deliberate design statement.
Always check the tile manufacturer’s recommendation for minimum joint width, as some large-format tiles require a specific minimum gap. Using joints that are too narrow can cause tiles to crack as the substrate expands and contracts.
Diagonal and Pattern Laying
Laying tiles at a 45-degree angle to the walls (diagonal laying) is a popular technique that can make a room appear wider and adds visual interest. However, it comes with a significant practical downside: far more cuts are needed at every edge of the room, and those cuts waste a large proportion of each tile.
For diagonal layouts, always use at least 20% wastage in your calculations. Some complex patterns (such as Versailles patterns, which combine multiple tile sizes, or herringbone patterns with rectangular tiles) may require even more. If you are planning a complex layout, consider asking the tile supplier to calculate the quantity based on the specific pattern.
The starting point for a diagonal lay is usually the centre of the room rather than a wall, to ensure the cut tiles at each edge are of equal width — this creates a symmetrical, professional finish.
Ordering Tiles: Practical Tips
Once you have your total tile quantity from this calculator, round up to the nearest full box. Box quantities vary by tile size — large format tiles (600×600mm) typically come in boxes of 3–5 tiles, while smaller tiles may come in boxes of 10–20. The box will state the number of tiles and the area they cover in m².
Key points when ordering:
- Check the batch/shade lot number on all boxes. Ensure every box has the same shade lot number so all tiles match.
- Order everything at once. If you need to order more later, the shade lot may no longer be available, and a new batch may be a slightly different shade.
- Check the tile grade. Grade 1 tiles are suitable for walls and light domestic floors. Heavy-duty commercial or outdoor tiles should be rated accordingly. Check the PEI rating (Porcelain Enamel Institute) for floor tiles — PEI 3 or above for most residential floors.
- Consider the rectified vs unrectified distinction. Rectified tiles are cut to precise dimensions after firing and allow tighter grout joints. Unrectified tiles have a natural variation of 1–2mm and require wider joints.
Related DIY Calculators
Once you have sorted your tiling, you may need to calculate other materials for your renovation project. Our Paint Calculator helps you work out how many litres of paint you need for walls and ceilings. The Wallpaper Calculator tells you how many rolls to buy based on your room dimensions and wallpaper repeat. For plastering a wall before tiling, try our Plastering Calculator to estimate the bags of plaster required.
If your tiling project is part of a wider refurbishment, the VAT Calculator is useful for checking what you owe if you are a sole trader claiming back VAT on materials, and the Salary Calculator can help you work out take-home pay if you are hiring a professional tiler.
Frequently Asked Questions
Divide the total area (m²) by the area of one tile including the grout gap, then add your wastage allowance (typically 10%). Round up to the nearest full box. This calculator does all of that automatically.
Use 5% for simple rectangular rooms with straight laying, 10% as a standard default, 15% for complex rooms with multiple cuts, and 20% for diagonal or pattern laying. When in doubt, go higher — unused full boxes can often be returned to the supplier.
300×600mm rectangular tiles are currently the most popular for UK bathroom walls. For floors, 600×600mm and 300×300mm are both widely used. Small mosaic tiles (100×100mm) remain popular for shower trays.
Avoid it wherever possible. Colour and texture can vary between production batches. Always buy all tiles from the same shade lot number (printed on the box) and order all you need at the same time.
It depends on tile size. A 600×600mm tile: ~2.8 tiles/m². A 300×600mm tile: ~5.6 tiles/m². A 300×300mm tile: ~11 tiles/m². This calculator works it out automatically for any size.