How do I calculate how many tiles I need?

Measure the total area you want to tile in square metres (length x width). Divide that by the area of one tile in square metres (tile length x tile width, converted from centimetres). Round up to the nearest whole tile. Then add a waste factor: 10% for straight grid patterns, 15% for diagonal or offset patterns, and 20% for complex shapes or large-format tiles. Always order whole boxes, rounding up to the next complete box.

What waste factor should I use for tiles?

10% is the standard recommendation for rectangular rooms laid in a grid pattern. Go to 15% for diagonal layouts, herringbone, or rooms with alcoves and angles. Use 20% for very large-format tiles (60cm+), natural stone, or rooms with many cuts around fixtures. Under-estimating the waste factor is the most common and expensive tiling mistake — you may not be able to get more tiles from the same batch later, and colour matching between production batches is notoriously inconsistent.

Should I order a whole box extra?

Yes, for two reasons. First, you almost certainly need the surplus during the job — cuts around pipes, door frames, and fittings are inevitable. Second, tiles crack years after installation. If you have spares from the same batch, a cracked tile is a quick swap. If you do not, you face a colour-matching problem that often means retiling the whole area. Keep any leftover tiles somewhere dry and label them with the supplier and batch number.

How do I tile a room that is not a simple rectangle?

Break it into rectangular sections and calculate each separately. An L-shaped room is two rectangles. A room with a bay window or alcove can be measured as the main rectangle plus or minus the irregular section. For curved edges or complex shapes, add 20% waste rather than 15% to account for the additional cuts. If there are built-in units or islands that will not be tiled, subtract their area — but include the perimeter cuts, which still require tiles.

What is the difference between floor tiles and wall tiles?

Floor tiles are generally thicker and designed to withstand foot traffic. Wall tiles are thinner, lighter, and often have a smoother back. Using wall tiles on a floor is a common mistake — they are not rated for the load and will crack or delaminate. You can use floor tiles on walls, though their greater weight requires appropriate adhesive. Always check the manufacturer's slip rating (R-rating) for floor tiles in wet areas: R10 is the minimum for a bathroom floor, R11+ for showers.

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How to Calculate Tiles for Any Floor or Wall Without Wasting Money

Getting tile quantity wrong is expensive: you either run short mid-project or end up with stacks of leftovers. This guide covers the maths, the waste factor, odd-shaped rooms, and why you should always keep a few spare tiles after the job is done.

7 April 2026

By Krishna Chaitanya, Software Engineer

The kitchen floor in my parents' house has a small patch near the back door where the grout colour does not quite match. It has been like that for fifteen years. The reason: when the original tiles ran out two-thirds through the job, the tiler ordered more from the same range but a different production batch. Identical code. Close enough colour in the showroom. Not close enough on the kitchen floor, where light catches them differently.

The fix would have cost about four boxes, roughly £80 at the time. Instead, the kitchen floor has been slightly wrong for a decade and a half because no one added the waste factor.

The maths here is quick. The part most guides skip is the waste factor: why it matters, how much to add, and what to do with whatever is left over after the job is done.

The real problem

Most people calculate tiles by dividing room area by tile area and ordering that many. That is the calculation that leaves you short.

The issue is cuts. Every edge of the room requires cut tiles. Every pipe, socket, doorframe, and fitting requires cut tiles. If you lay tiles diagonally, every single row touching a wall requires a cut tile. Cuts account for 10-20% of all tiles laid in practice. The larger the room and the simpler the layout, the closer to 10%. The more complex the room, the closer to 20%.

There is also breakage. Natural stone chips during cutting. Porcelain splinters along unexpected lines. Budget tiles from some ranges have inconsistent dimensions that force adjustments. If you are cutting tiles yourself with a hired cutter rather than a wet saw, expect more breakage than a tiler would produce.

The waste factor accounts for both. Get it right upfront and you avoid the mid-project drive back to the tile shop.

The calculation

Step 1: Measure your area

For a rectangular room, measure the length and width at floor level in metres and multiply them. Include the area under any furniture that will be removed during tiling — kitchens and bathrooms are typically tiled fully under units in case they are ever replaced.

If the room is not rectangular, split it into rectangular sections, calculate each area separately, and add them together.

For walls, measure each section you want to tile. Subtract large openings like windows, but not smaller ones like plug sockets — those are too small to affect the count and require cut tiles around them anyway.

Step 2: Calculate tiles needed (before waste)

Convert your tile dimensions from centimetres to metres:

A 30x60cm tile has an area of 0.3 x 0.6 = 0.18 m²
A 60x60cm tile has an area of 0.6 x 0.6 = 0.36 m²
A 10x30cm subway tile has an area of 0.1 x 0.3 = 0.03 m²

Divide your room area by the tile area and round up.

Example: 14.5 m² room / 0.18 m² per tile = 80.5, round up to 81 tiles

Step 3: Add the waste factor

Tile installation showing cuts around edges and fixtures

Layout	Waste factor
Grid pattern, rectangular room	10%
Offset / brick pattern	10-12%
Diagonal (45°)	15%
Herringbone	15-20%
Large format tiles (60cm+)	15-20%
Natural stone	15-20%
Complex room (alcoves, angles)	15-20%

Example continued: 81 tiles x 1.10 (10% waste) = 89.1, round up to 90 tiles

Step 4: Convert to boxes

Check the box label for how many tiles it contains. Divide your required tile count by tiles per box and round up.

Example: 90 tiles / 12 tiles per box = 7.5, order 8 boxes

The Tile Calculator does all of this automatically: input your room dimensions, tile size, and layout pattern, and it gives you the number of boxes to order.

Worked example

Project: Bathroom floor and lower half of walls

Floor:

Room: 2.4m x 3.2m = 7.68 m²
Tile: 30x60cm (0.18 m² each)
Tiles before waste: 7.68 / 0.18 = 42.7, round up to 43 tiles
Waste (10%, grid pattern): 43 x 1.10 = 47.3, round up to 48 tiles
Box size: 8 tiles/box → 6 boxes

Walls (lower half, 1m high, four walls, minus door opening):

Perimeter: (2.4 + 3.2) x 2 = 11.2 linear metres
Door opening: 0.9m wide x 1m high = 0.9 m² (subtract)
Wall area: (11.2 x 1m) - 0.9 = 10.3 m²
Tile: 10x30cm subway tile (0.03 m² each)
Tiles before waste: 10.3 / 0.03 = 343.3, round up to 344 tiles
Waste (12%, brick pattern): 344 x 1.12 = 385.3, round up to 386 tiles
Box size: 44 tiles/box → 9 boxes

Total to order: 6 boxes floor tiles, 9 boxes wall tiles. Run the same numbers through the Tile Calculator before heading to the tile shop.

Common mistakes

Not accounting for grout lines. Most tile area calculations use the tile face dimension, not including grout joints. Grout lines are typically 2-5mm, which adds slightly to coverage. For most jobs the difference is small enough to ignore, but for feature panels or mosaic borders, factor joint width into your spacing.

Measuring at head height for floors. Floor dimensions should be measured at floor level, not from the top of the skirting board or a metre off the ground. Rooms are rarely perfectly square, and measuring in the wrong place introduces errors that affect cut planning.

Ordering different tiles for repairs later. The same reference code from the same manufacturer can look different between production runs. If you are ordering a spare box for future repairs, which you should, order it at the same time as your main order from the same batch. Some suppliers will indicate the batch number on the box.

Ignoring adhesive and grout quantities. Most adhesives cover around 4-5 m² per bag at standard 6mm notch depth, but large-format tiles need more adhesive and sometimes back-buttering as well. Grout coverage depends on tile size and joint width: smaller tiles with tight joints use significantly more grout than large-format tiles. Check manufacturer coverage rates before purchasing.

What to do with leftover tiles

Keep them. Store them somewhere dry, flat or on edge, not stacked face-to-face without protection. Write the tile reference, supplier, and batch number on a piece of tape and stick it to the box.

When a tile eventually cracks or chips, and in a bathroom or kitchen one eventually will, you have a ready replacement from the same batch. Without those spares, a single cracked tile becomes a colour-matching problem that can mean retiling the whole area.

For a large room, the waste factor means you should end up with only a few tiles spare after the job. That is the right outcome. You want to finish close to zero surplus, not be sitting on two full boxes. The calculation is designed to give you just enough, not a comfortable safety margin on top.