Working out tiles is a coverage problem: how many tiles of a given size cover a given area, plus a margin for the tiles you'll cut and break. Divide the area by the area of one tile and you have the bare count; the grout gap nudges it down a fraction because each tile plus its joint covers a little more floor, and the wastage allowance nudges it back up for cuts at the edges. Round the result up to whole boxes and keep a few spare — matching a batch years later is nearly impossible.
Reviewed: June 19, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: area-coverage tiling estimation practice.
The tiling equations
Keep units consistent: convert tile millimetres to metres (300 mm = 0.3 m) before dividing into a square-metre area, or the count will be off by a factor of a million. The grout gap is added to both tile dimensions because the joint surrounds every tile. Wastage is a simple multiplier — 1.10 for 10% — and both the tile count and the box count always round up, never down.
Worked example — a 20 m² floor
Scenario: A 4 m × 5 m floor (20 m²) tiled with 300 × 300 mm tiles, 3 mm grout, 10% wastage, 11 tiles per box.
The floor needs about 240 tiles after a 10% allowance, which is 22 boxes of 11. Without the grout gap the bare count would be 222 tiles, so the joint saves a handful. Switch to a diagonal lay and bump the wastage to 15% — that pushes the order to about 250 tiles and 23 boxes, because angled cuts leave more unusable offcuts.
Frequently Asked Questions
area ÷ tile area, plus wastage. 20 m² with 300×300 tiles ≈ 222 bare, ~245 with 10%.
~10% straight lay, ~15% diagonal/patterned. Big tiles in awkward rooms waste more. Keep spares for repairs.
A little — each tile plus joint covers slightly more, so you need marginally fewer. A 300 mm tile + 3 mm gap covers 303 mm.
tiles ÷ tiles per box, rounded up. 245 tiles at 11/box = 23 boxes. Use one batch number for shade.
Same method: height × width per wall, subtract openings, divide by tile area, add waste. Wall tiles are often a different size.