Tile calculations require more than just measuring the floor. Here's the formula for any room shape, how much to add for waste, and why ordering the right amount the first time matters.
Running out of tiles mid-job and finding the same batch is no longer available is one of the most frustrating DIY experiences. Getting the order right requires a proper calculation, not a rough guess.
Step 1: Measure the room. For a rectangular room, length × width = area in m². For L-shaped or irregular rooms, split into rectangles, calculate each, and add together.
Step 2: Calculate tile area. A standard 600mm × 600mm tile = 0.6 × 0.6 = 0.36m².
Step 3: Divide room area by tile area.
Step 4: Add a wastage allowance. Always add extra for cuts, breakages, and future repairs.
Tiles from the same manufacturer can vary slightly in shade between production batches (called lots or dye lots). If you run out mid-job and reorder, the new tiles may be noticeably different when the room is finished — the difference is visible in natural light even if the tiles look identical in the shop.
Always note the lot/batch number on the tile packaging. If ordering online, specify you need all tiles from the same batch. And order enough. Storing 4–5 extra tiles is far cheaper than regretting it.
Grout quantity depends on tile size, joint width, and tile thickness. A general rule for floor tiles:
Most bags of grout state their coverage on the packaging — this formula is a cross-check. Always buy slightly more than the estimate, as grout can be mixed with varying consistency.
Standard flexible tile adhesive covers approximately 3–4m² per 20kg bag for floor tiles (less for wall tiles or large format tiles). For the example room of 14.4m²: roughly 4 bags of 20kg adhesive, allowing for the adhesive bed thickness.
Large format tiles (600mm+) require back-buttering as well as floor coverage, which increases adhesive consumption by 20–30%.