Tile calculator
Work out how many tiles to order, how much adhesive and grout you need with them, and what the whole job costs — with the waste allowance set by your actual laying pattern rather than a flat 10%.
How this calculator works
1. Net area, then waste — in that order
Most tile calculators multiply length by width and add a flat 10%. That is right for a plain grid in a square room and wrong for everything else. Waste is not a property of the room, it is a property of the cut: every tile that meets a wall, a door frame or a corner gets cut, and the offcut is usually unusable. A pattern that forces more cuts per square metre wastes more material.
So this calculator builds the allowance from three separate things and adds them together:
- Pattern waste — 10% for a straight grid, up to 18% for herringbone. The full table is on the waste factor reference page.
- Shape penalty — 0%, 2% or 5%, depending on how many cut-outs the room has.
- Small-room penalty — up to 6% under 3 m², because one ruined cut in a small bathroom is a much bigger share of the order.
2. Tiles, not area
You buy tiles, not square metres. The calculator converts the padded area into whole tiles using the tile's footprint including its joint — a 600 × 600 mm tile with a 3 mm joint occupies 603 × 603 mm on the floor, not 600 × 600. Over a 40 m² floor that difference is about one tile in every hundred. It then rounds up to whole boxes, because that is how the merchant will sell them to you.
3. Grout is derived, not guessed
Grout quantity comes out of the geometry rather than a lookup table. For a tile A × B with joint width W, each tile plus its share of the surrounding joint occupies (A+W)(B+W). The joint's share of that footprint is:
f = 1 − (A × B) / ((A+W) × (B+W))
grout kg per m² = tile thickness (mm) × f × grout density (g/cm³)
Set cement grout at 1.6 g/cm³. A 600 × 600 × 10 mm porcelain tile with a 3 mm joint gives f = 0.0099, so 10 × 0.0099 × 1.6 = 0.16 kg per m² — which is what the manufacturers' own charts say. The advantage of deriving it is that it stays right for tile sizes and joint widths no chart covers.
4. Adhesive follows the trowel, not the tile
Adhesive consumption is set by the notch depth of the trowel you spread it with, and the notch is chosen from the tile size. A 6 mm notch puts down about 3 kg per m²; a 12 mm notch about 6 kg. The calculator picks the notch from your tile's equivalent side — the square root of its area, which handles plank formats correctly where a longest-edge rule does not — lets you override it, and adds 25–40% if you tell it the substrate is uneven. Figures are on the adhesive and grout coverage page.
Order everything in one go. Tiles are made in batches and batches vary in shade. If you run short and re-order later you will very likely get a different batch, and the difference is visible under a window. This is the single most common way a tiling job goes wrong, and the reason the waste allowance exists.
What the calculator does not cover
- Levelling compound, backer board, tanking and primer. These depend on the substrate, not the tile, and are priced separately.
- Trims, edge profiles and thresholds. Measure these as linear metres of exposed edge.
- Silicone. Every internal corner and every junction with a bath, tray or worktop is silicone, never grout. A 310 ml cartridge runs roughly 6–8 linear metres at a typical bead.
- Underfloor heating. Mat or cable systems change adhesive consumption significantly — you are filling around the element as well as bedding the tile.
Common questions
Is 10% waste enough?
For a straight grid in a rectangular room with a competent tiler, yes. For a diagonal layout, herringbone, a room full of cut-outs, or a small bathroom, no — and running short mid-job means a batch mismatch you cannot fix. The pattern is the main driver: diagonal costs you about 15%, herringbone about 18%, because almost every perimeter tile is a compound cut.
Should I deduct the area of a bath or a kitchen island?
Deduct it only if the tile genuinely stops at the edge and is not continued underneath. Many installers run tile under a freestanding bath or a removable appliance so the floor still works if the fitting changes later. If in doubt, do not deduct: buying 4% extra tile is much cheaper than a second delivery in a different shade.
Why does the tile count use 603 mm for a 600 mm tile?
Because the grout joint is part of the repeating unit. Each tile occupies its own size plus one joint width in each direction. Ignoring it over-counts tiles slightly — harmless on its own, but it compounds with the waste allowance and can push you into an extra box you do not need.
How much extra should I keep for repairs?
One full box, stored flat and dry, for anything you would be upset to lose. Tile ranges are discontinued constantly, and a single cracked tile with no matching spare can mean re-tiling the whole floor. Tick the spare box option and the calculator adds it to the order.
Does the adhesive figure include back-buttering?
No. Large-format tiles over 600 mm normally need back-buttering to reach the coverage the standards require, which roughly adds a third again to adhesive consumption. If you are back-buttering, set the substrate to "uneven" as a rough proxy, or pick the next trowel size up.
Related
- Waste factor reference table — every pattern, with the reasoning
- Adhesive and grout coverage tables
- Flooring calculator — for laminate, vinyl plank and engineered wood
Method last reviewed 2026-09-18. Figures are estimates for planning; check your supplier's technical data sheet before ordering.