How many tiles do you need,
down to the last box.

Field guide

How to calculate tile quantity and why you always need more than you think.

Step 1: Measure the area accurately

For a rectangular room, the area is simply length × width. Measure to the nearest centimetre or eighth of an inch and use the largest dimension, not the smallest. You want to plan for the full area including cuts.

For L-shaped or irregular rooms, break the space into rectangles, calculate each area separately, and add them together. For rooms with permanent fixtures (islands, fireplaces, built-ins) you can subtract their footprint, but only if the tiles won't be cut to fit around them. Cut tiles count as waste.

Don't forget: measure the actual tiled area, not the room's overall floor plan. If baseboards will cover 10 cm (4 inches) on each side, you may be able to reduce the tiled area slightly, but most installers recommend measuring to the wall anyway to give yourself more material.

Step 2: Account for grout lines

Tiles are never installed edge to edge. A grout joint (grout line, grout gap) is intentionally left between tiles and later filled with grout. The joint serves several purposes: it compensates for slight variations in tile size (especially rectified tiles), allows for thermal expansion and contraction, and is essential for waterproofing in wet areas.

Typical grout joint widths by tile type:

• Rectified tiles (precision-cut): 2–3 mm (1/16–1/8 in)
• Standard floor tiles (12"×12", 18"×18"): 3–4 mm (1/8–3/16 in)
• Larger format tiles (24"+ / 60 cm+): 4–6 mm (3/16–1/4 in)
• Natural stone: 3–6 mm depending on variation

This calculator adds the grout gap to both the tile length and width when computing the effective tile area, which correctly accounts for the grout in the coverage calculation.

Step 3: Add a waste allowance: always

No installation is perfect. Tiles must be cut to fit edges, corners, and around obstacles. Some tiles may crack during cutting. Some may arrive damaged. And you always want extra tiles for future repairs, because matching discontinued tiles years later is nearly impossible.

Standard waste percentages by installation type:

• 5%: Professional installation, simple rectangular room, straight layout. Only appropriate when the installer is confident in their cuts and the project is very straightforward.
• 10%: The standard recommendation for most residential projects. Accounts for typical cuts, breakage, and a small stockpile for repairs.
• 15%: Complex cuts (many alcoves, toilets, radiators), diagonal (45°) layout, or natural stone with variation.
• 20%: Herringbone, brick/offset, or complex mosaic patterns where a larger proportion of each tile is cut.

The 10% rule is widely recommended by tile manufacturers, installers, and retailers. Ordering too few tiles is a much more expensive mistake than ordering slightly too many. Leftover tiles have storage value; a project halted by short supply does not.

How grout gap affects tile count

For small tiles in large areas, the grout gap has a negligible effect on tile count. For large-format tiles, it matters more. Example:

• A 60 cm × 60 cm tile with a 4 mm gap has an effective area of 60.4 cm × 60.4 cm = 3648.16 cm² versus 3600 cm² (1.3% larger). Over 100 tiles, you'd need 1–2 fewer tiles than if you ignored the gap.
• A 10 cm × 10 cm mosaic tile with a 3 mm gap has effective area 10.3 cm × 10.3 cm = 106.09 cm² versus 100 cm² (6.1% larger). Ignoring the gap for small tiles significantly overstates the tile count.

Reading tile packaging: coverage area vs tile count

Tile boxes often list both the number of tiles and the coverage area (e.g., "15 tiles, covering 13.5 sq ft"). This coverage is typically calculated at a standard grout joint width (often 3/16 in for floor tiles). If your grout joint differs significantly, your actual coverage will vary.

When ordering: always round up to the nearest full box. Partial boxes are non-returnable at most retailers. If the calculator shows 14.2 boxes, order 15.

Diagonal (45°) and pattern layouts

Installing tiles diagonally, at a 45° angle to the walls, is a popular design choice that makes a room appear wider. The trade-off is increased waste: every edge of the room requires a diagonal cut, using approximately twice the length of tile versus a square cut. The actual waste percentage depends on room shape and tile size, but 15% is a reliable minimum for diagonal layouts.

Herringbone and brick (offset) patterns also generate more waste due to the number of half-tiles required at edges. Use 15–20% waste for these patterns.