Tile Calculator

What's the key thing to understand about Waste Allowance Guide?

Buying exactly the area you need is a classic DIY mistake — every tiling job needs an allowance for offcuts, breakages, and mistakes, and the right percentage depends on how the tiles will be laid. Straight lay (tiles aligned in a simple grid, the most common pattern): add 10% to your area. Diagonal lay (tiles rotated 45° to the wall, creating a diamond pattern): add 15%, because more tiles need cutting at the edges. Complex patterns like herringbone, mosaic, or random sizing: add 20% or more. The percentage compounds with room shape too — a perfectly square room with whole rows of edge cuts wastes less than an awkward L-shape or a room with multiple alcoves and obstacles like a toilet, sink, or built-in unit. A worked example: a 12 m² bathroom in straight lay needs 13.2 m² of tiles (12 + 10%), but the same room in diagonal lay needs 13.8 m², and in herringbone 14.4 m². Beyond the percentage, always order at least one extra box from the same batch code — tiles get discontinued, batches sell out, and finding matching replacements years later for a future repair is often impossible. Storing a spare box in the loft costs you the price of the box, but having no matching tile when one cracks can mean retiling the whole room. The right waste allowance is cheap insurance compared with running short mid-job.

What should I know about Grout Gap Tips?

The width of the grout gap affects both the look and the total tile count more than most people expect, especially at small variations. The standard guidance: wall tiles in bathrooms and kitchens typically use 1.5–3 mm gaps; large floor tiles use 3–5 mm; outdoor tiles and natural stone use 5 mm or more to allow for movement and irregularities in the stone. The wider the gap, the fewer tiles you need to cover the same area (and the more grout you'll use). A 200 mm × 200 mm tile at a 2 mm gap occupies 202 × 202 = 40,804 mm² of wall area including its share of grout; at a 5 mm gap it occupies 205 × 205 = 42,025 mm² — about 3% fewer tiles per square metre. On a large job, that adds up. Smaller gaps give a sleeker, more modern look and reduce visible grout maintenance; wider gaps suit rustic or natural stone aesthetics and allow more tolerance for irregular tile sizes. Spacers come in 1, 1.5, 2, 3, 4, 5, 8, 10 mm and beyond — pick the size that suits your tiles and look. Don't use a gap smaller than your tiles allow: rectified tiles (machine-cut to precise sizes) can take very small gaps (1 mm); pressed or hand-made tiles need wider gaps (3 mm+) to accommodate their natural size variation. For floor tiles, narrower gaps look cleaner but show every imperfection in your tile alignment — wider gaps are more forgiving for DIY-level installation.

What's the key thing to understand about Batch Numbers?

Tiles from different manufacturing batches can have subtle variations in colour, size, and surface texture that aren't obvious in the shop but become glaringly visible once laid side by side on your wall or floor. This is because tile manufacturing involves natural materials (clay, glaze, pigment) whose properties drift slightly between production runs — the same tile design made on Tuesday and made on Friday can be marginally different. The fix is simple: always check the batch number (sometimes called dye lot or shade code) printed on every box, and make sure all your boxes match. If a shop tries to make up your order from mixed batches, ask them to find boxes from one batch or order more from the original batch. For floor tiles in particular, the size variation between batches can be enough that 600 mm tiles from one batch are actually 599 or 601 mm — within manufacturing tolerance but enough to misalign joints across batches. If you must use mixed batches (because one is short), mix the tiles randomly across the job rather than tiling with one batch in one area and another batch elsewhere, so any variation blends in rather than appears as an obvious line. Keep the box labels until the job is finished — they have the batch code you'll need if you have to buy more mid-project, and the leftover tiles should be stored in their original box with the label intact for future repairs. The same logic applies to grout: mix all your bags in advance and aim to grout the whole job in one session, since grout colour can vary between bags and batches even more than tiles.

What's the key thing to understand about Choosing Tiles for Different Rooms?

Tile selection should match the demands of the space. Porcelain (0.1-0.5% water absorption) is virtually impervious — ideal for bathrooms and kitchens. Slip resistance: floors need a minimum R9-R11 rating for wet areas. Large-format tiles (600x600mm and above) use 3-5mm joints with a polymer-modified adhesive. Rectified tiles (precision cut to exact size) can use joints as small as 1mm for a near-seamless look. Always confirm underfloor heating compatibility with large-format tiles — the coefficient of thermal expansion in large tiles means they need a flexible adhesive rated for underfloor heating and a proper expansion gap at room boundaries, or the tiles can crack as the floor heats and cools. Check the tile and adhesive manufacturer's specifications together rather than assuming any large tile is automatically compatible.

Worked Example: Tiles Needed for a 3.5m x 2.8m Bathroom Floor

A bathroom floor measuring 3.5m x 2.8m (9.8 square metres) using a 300mm x 300mm (0.09 square metre) tile shows how waste allowance and box sizing combine to determine the real order quantity, not just the raw area.

Rounding up to full boxes at the end, rather than ordering the exact calculated tile count, is essential because tile retailers sell by the box, not by the individual tile, and the final box-rounding step here adds one extra tile (121 vs the 120 calculated) almost for free — well worth it as a buffer against breakage or a cutting mistake discovered partway through the job. A diagonal (herringbone or 45-degree) layout would push the waste allowance from the 10% used here up to 15-20%, since diagonal cuts at the room's edges waste proportionally more of each cut tile than a straight lay.

Rectified vs Non-Rectified Tiles and Why It Changes the Grout Line

Rectified tiles are mechanically cut and ground after firing to give precisely uniform dimensions and perfectly square edges, in contrast to non-rectified tiles, which keep the slightly rounded, less perfectly uniform edge that comes straight out of the kiln. This distinction is not just a quality label — it directly affects how the tiling job should be planned. Rectified tiles allow a much narrower grout line (sometimes as little as 1.5-2mm) because their edges align precisely, giving a more seamless, modern look often sought for large-format floor and wall tiles. Non-rectified tiles need a wider grout line (typically 3mm or more) specifically to absorb the natural, slight dimensional variation between tiles — fitting non-rectified tiles with a too-narrow grout gap makes any size inconsistency between tiles highly visible as uneven lines, since there's no grout width left to disguise the variation. This has a direct, if sometimes overlooked, effect on quantity calculations: a tighter grout gap on rectified tile means very slightly more tile and very slightly less grout covers the same floor area compared with the wider gap used for non-rectified tile of the same nominal size, and large-format rectified tiles (600mm+ or 900mm+ formats, increasingly common for contemporary floors) also typically need a higher waste allowance for cutting, since fewer, larger tiles are used to cover the same area, meaning each individual cut mistake wastes a larger proportion of the total tile count than it would with a smaller format.