Your measurements
Results
Fill in every measurement above and your results will appear here.
Your shopping list
| Material | Quantity | Notes |
|---|
How the tile calculator works
Tiles are sold by the box, not by the tile, and a box is not a fixed area: it holds a number of tiles, so what it covers depends on how big they are. That is why the calculator takes the tile size and the box coverage as separate figures. The tile size tells it how many whole tiles the job needs; the box coverage tells it how many boxes to buy. The m² figure is printed on every box label, so read it off the one you are buying rather than trusting a default — a box of 300 × 300 mm tiles and a box of 600 × 600 mm tiles do not cover the same floor.
Start with the surface. A wall or a floor is length × width, and an L-shape is two rectangles measured separately and added together. Then add the cutting waste: every tile cut at an edge, a door, a socket or a pipe comes out of a whole tile, so the order rounds up twice — once for the whole tiles the cuts consume, and again for the box.
Cutting waste is the figure that catches people out
Ten per cent is the cautious figure for a straight lay in a single room, and it is the default here. Set the tiles diagonally, run a herringbone, or work around a lot of obstacles, and 15% is a better allowance. If the tiles are a clearance line or a shade lot you cannot buy again, allow 15% and keep a spare box: matching a batch later is usually impossible, and a repair ten years from now depends on having one.
The calculator rounds up, always. You cannot buy two-thirds of a box, and a part tile is still a whole tile off the box, so an order that lands on 13.2 boxes is bought as 14. The spare that leaves is normal — the offcut box does the next job, a repair, or goes in the loft.
Adhesive, grout and spacers
Adhesive, grout and spacers are the three things that stop a job halfway. As a planning estimate, allow roughly 4 kg of adhesive per square metre at a 3 mm bed, which is about 5 m² from a 20 kg bag. A deeper bed, a large-format tile or an uneven wall all take more, so treat that as a starting point and check the bag.
Grout is different: it fills the joint, so the quantity depends on the tile size, the joint width and how deep the joint is filled rather than on the floor area alone. Small tiles and wide joints mean much more grout; large-format tiles and tight joints mean less. Buy a bag more than you think you need — running out halfway up a wall is worse than a spare bag in the cupboard.
Spacers sit where four tiles meet, so count the crossings inside the grid rather than the tiles themselves. A 4 m × 3 m floor in 300 mm tiles is 14 across and 10 down, which is 117 crossings: one bag of 250 does the room with plenty to lose.
Tile FAQs
How many tiles do I need for a wall or floor?
Divide the surface area by the area of one tile. A 4 m × 3 m floor is 12 m², and a 300 × 300 mm tile covers 0.09 m², so 12 ÷ 0.09 is about 133 tiles before any allowance. Add the cutting waste, because every edge cut consumes a whole tile: at 10% that is 147 tiles. The calculator does this for you and rounds up, because a part tile is bought as a whole tile.
How much extra should I allow for cutting waste?
About 10% for a straight lay in one room, which is the default here and the cautious figure. A diagonal or herringbone layout takes nearer 15%, and a room with a lot of obstacles, or a tile you may not be able to buy again, is worth 15% too. Keep one full box back on a large order for later repairs.
How much tile adhesive do I need?
As a planning estimate, allow about 4 kg per square metre for a 3 mm bed, so a 20 kg bag covers roughly 5 m² — a 12 m² floor is about three bags. That is an estimate only: a deeper bed, a large-format tile or an uneven wall all take more, and the maker's bag states what it covers. Always check the product data before ordering.
How much grout do I need?
Grout fills the joint, so the amount depends on the tile size, the joint width and how deep the joint is filled, not on the floor area alone. For a 300 × 300 mm tile with 3 mm joints, the joints are about 2% of the surface, which works out at roughly 3.3 kg of grout for 12 m². Mosaic tiles have far more joint and take much more grout; large-format tiles take less.
How many tile spacers do I need?
A spacer sits where four tiles meet, so count the crossings inside the grid rather than the tiles. A 4 m × 3 m floor set out in 300 mm tiles is 14 tiles across and 10 down, which is 13 × 9 = 117 crossings. Spacers are sold in bags of 250 as a rule, so one bag normally does a room — and you will lose some.
Why does the coverage of a box of tiles vary?
Because a box holds a number of tiles, not a fixed area. A box of 300 × 300 mm tiles often covers around 1 m², while a box of 600 × 600 mm tiles holds fewer, larger tiles and covers a different area again. Read the m² figure on the box you are buying and type it into the calculator rather than relying on the default.
Regs & planning for this calculator
Tiling is decorating, but three rules on the site's reference library bite on the room it happens in.
- Approved Document P — the special location around a bath or shower. Diagram 2 carries the note that socket-outlets should not be located within 3 m of a bath tub or shower tray, and it is the figure that most often kills a layout after the tiling is up. Read the requirement.
- Approved Document E — impact sound. A purpose-built separating floor has a 62 dB L′nT,w maximum, and the floor finish is part of that build-up, so a tiled floor in a flat is not a purely cosmetic choice. Read the requirement.
- Approved Document C — keeping the floor dry. The damp-proof course should sit at least 150 mm above the adjoining ground, and a ground floor should be built so its thermal transmittance does not exceed 0.7 W/m²K, which is why a tiled ground floor over a cold slab feels the way it does. Read the requirement.