How many tiles a room needs, and how many to buy
How to work out tiles and boxes for a floor or wall, why a 600 mm tile is not 4 square feet, how much wastage to allow for each layout, and how to compare prices quoted per box and per square foot.
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In short
- Tiles = floor area ÷ area of one tile, then add wastage and round up. Shops sell whole boxes, so round up again.
- A 600 × 600 mm tile covers 3.88 sq ft, not 4, because 600 mm is shorter than 2 feet. On a large floor that is several extra tiles.
- Allow about 10 percent for straight laying, 5 percent for simple small-tile rooms and 15 percent for diagonal laying.
- A 15 × 12 ft room with 600 mm tiles takes 47 tiles, 52 with wastage, which is 13 boxes of four.
- Buy a little spare from the same batch, because shades vary between batches and a repair may need a match years later.
Tile is one of those purchases where a small error is expensive in both directions. Too few, and the last corner of the room waits a week for a box that may not match. Too many, and unopened boxes sit in a store room. The sum itself takes a minute, but it has two traps: nominal sizes that are not quite what they sound like, and shops that sell by the box while quoting by the square foot.
The sum
tiles = floor area ÷ area of one tile
Then add wastage and round up:
tiles to buy = tiles × (1 + wastage ÷ 100)
Then convert to boxes, rounding up again:
boxes = tiles to buy ÷ tiles in a box
Take a room 15 ft by 12 ft, which is 180 sq ft, with 600 × 600 mm tiles. One tile covers 3.88 sq ft, so the room takes 47 tiles. Adding 10 percent gives 52. At four tiles to a box, that is 13 boxes, which cover 201.5 sq ft in all.
Why 600 mm is not 2 feet
Tiles are sold under both metric and imperial names, as if they were the same. They are not. Two feet is 609.6 mm, so a 600 mm tile is about 10 mm short on each side. It covers (600 ÷ 304.8)² = 3.88 sq ft rather than 4. That looks trivial until you divide a large floor by the wrong number: 1,000 sq ft takes 250 tiles at 4 sq ft each, but 259 at 3.88.
The calculator works from the real size in millimetres, so it gets this right. If you lay out a room with a tape, use the actual size printed on the box, not the name.
| Tile | Area of one tile | Tiles per 100 sq ft | With 10% wastage |
|---|---|---|---|
| 300 × 300 mm | 0.97 sq ft | 104 | 114 |
| 300 × 600 mm | 1.94 sq ft | 52 | 57 |
| 600 × 600 mm | 3.88 sq ft | 26 | 29 |
| 600 × 1200 mm | 7.75 sq ft | 13 | 15 |
| 800 × 800 mm | 6.89 sq ft | 15 | 16 |
How much wastage
Wastage covers cut tiles at the walls, breakage in transport and handling, and mistakes. It depends more on the layout than on the room size.
- 5 percent: small tiles in a simple rectangular room with few cuts.
- 10 percent: the usual allowance for a straight layout.
- 15 percent: diagonal laying, where every wall edge is a cut, or large format tiles, which break more easily and leave bigger offcuts.
An irregular room, with niches and pillars, needs more. Patterned tiles that must match a repeat need more again, because a cut piece often cannot be reused elsewhere.
A small bathroom can take a surprising share of wastage. In a tiny room, every tile near a wall is a cut, so the percentage is higher than on an open floor. For a room under about 40 sq ft, add a few percent more than you otherwise would.
Boxes and the price per square foot
Shops usually quote a price per square foot but sell only whole boxes. The two are linked by the box's coverage, which is printed on it. A box of four 600 mm tiles covers 15.5 sq ft. If the price is ₹60 per sq ft, a box costs about ₹930.
This is why the calculator costs the boxes rather than the bare floor area. For the 180 sq ft room, you pay for 201.5 sq ft even though the floor is smaller. Comparing two tiles by price per sq ft alone can mislead, because the size of the box and the rounding up change what you pay.
Tiles per box vary between brands, even for the same nominal size. Change the number in the calculator to match the box you are buying. Some suppliers will return unopened boxes, but check that before relying on it.
Measuring a room that is not a rectangle
Split the room into rectangles, work out each area and add them. An L-shaped room is two rectangles, as the area calculator shows. Subtract anything that will not be tiled, such as a built-in cupboard, but only if it is permanent and already in place. Measure at floor level and note any wall that is out of square, since a sloping wall forces a tapering row of cuts along it.
Walls and skirting
The same sum works for walls. Take each wall's width times the tiled height, subtract doors and windows, and add the results. A bathroom 5 × 8 ft with walls tiled to 7 ft has a perimeter of 26 ft and a wall area of 182 sq ft before openings. That is often three times the floor, which is why wall tiles are usually the larger part of a bathroom's bill.
Skirting is usually cut from floor tiles. A 600 mm tile cut into 100 mm strips gives six pieces, or 3.6 m of skirting per tile. For a room with a 54 ft perimeter, less a 3 ft door, that is about 15.5 m of skirting, so five tiles. Add them to the count.
Other things to buy
Tiles are only part of the job. Tile adhesive or a cement bed goes under them, and the amount depends on the thickness and the floor's evenness. Grout fills the joints, and narrow joints on large tiles use little. Leave a spacer gap as the maker recommends. Rectified tiles allow thinner joints than ordinary ones. Bedding quantities can be estimated with the cement calculator.
Keep a few spare tiles when the job is done. Tiles from a later batch can differ noticeably in shade, and replacing one cracked tile years later is far easier from your own store.
Common room sizes
These figures use 600 × 600 mm tiles, 10 percent wastage and boxes of four. Each row is rounded up to whole tiles and whole boxes, which is how you will buy them.
| Room | Floor area | Tiles | With wastage | Boxes |
|---|---|---|---|---|
| 10 × 10 ft | 100 sq ft | 26 | 29 | 8 |
| 12 × 10 ft | 120 sq ft | 31 | 35 | 9 |
| 12 × 12 ft | 144 sq ft | 38 | 41 | 11 |
| 15 × 12 ft | 180 sq ft | 47 | 52 | 13 |
| 20 × 15 ft | 300 sq ft | 78 | 86 | 22 |
Notice that the number of boxes does not rise smoothly with the area. A slightly larger room can still fall inside the same box count, and the spare tiles that result are useful later.
Mistakes to avoid
Using 4 sq ft for a 600 mm tile. This understates the count by about 3 percent, as shown above.
Forgetting a room next door. If a passage or balcony uses the same tile, order it together. A second order may come from a different batch, and the shade can differ.
Measuring only once. Rooms are seldom perfect rectangles. Measure each wall at floor level and use the longer of two opposite sides.
Mixing lots. Check that the shade and size codes printed on every box match before the tiler opens them. A mismatch found after laying is expensive to put right.
Skipping the dry layout. Laying a row without adhesive shows where the cuts will fall. A thin sliver along a visible wall looks poor, and shifting the starting line can avoid it, although it can change the wastage slightly.
What this calculator assumes
- The room is a rectangle, measured in one unit.
- The tile size in millimetres is the real size. Grout joints are ignored, since a thin joint changes the count very little.
- Boxes are bought whole, and the cost is for all the boxes rather than just the floor area.
- Wastage is a flat percentage of the tile count.
- Bedding, adhesive, grout, skirting and labour are not included.