Tile Calculator (tiles, boxes, grout)

Understanding the tile calculator — concept and principle

This calculator estimates how many tiles and boxes to buy for a floor or wall, plus rough quantities of grout and tile adhesive. It accounts for the grout joint around each tile and adds a waste allowance for cuts and breakage.

Measure one tile with its joint, divide the area, add 10% and round up to whole boxes.

How it is calculated

Tile footprint = (length + joint) × (width + joint), converted to m² (cm ÷ 100, mm ÷ 1,000).
Tiles = area ÷ footprint × (1 + waste%), rounded up.
Boxes = tiles ÷ tiles per box, rounded up.
Grout (kg) ≈ (L + W) ÷ (L × W) × joint width × joint depth × 1.6 × area, with L and W in mm and joint depth taken as the tile thickness. The result per m² comes out in litres, and 1.6 kg/L is the assumed density of mixed grout.
Adhesive (kg) ≈ area × 4 kg/m².

The principle

Each tile "owns" a rectangle that includes half of the joint on every side, which is the same as one tile plus one full joint width in each direction; dividing the area by that rectangle gives the tile count. For grout, every metre of joint is a thin channel of width × depth. In one square metre, a grid of L × W tiles contains about 1/L + 1/W metres of joint per metre, which is where (L + W)/(L × W) comes from. Multiplying by width and depth gives volume, and density turns volume into mass.

Worked example

Area 12 m², tiles 60 × 30 cm, 3 mm joint, 10% waste, 8 tiles per box, 9 mm thick.
Footprint = 0.603 × 0.303 = 0.182709 m².
Tiles = 12 ÷ 0.182709 = 65.68; × 1.1 = 72.25, rounded up to 73 tiles.
Boxes = 73 ÷ 8 = 9.125, rounded up to 10 boxes (80 tiles).
Grout = (600 + 300) ÷ (600 × 300) × 3 × 9 × 1.6 × 12 = 0.005 × 27 × 1.6 × 12 ≈ 2.59 kg.
Adhesive = 12 × 4 = 48 kg.

Each point is the calculator re-run with only “Tile length (cm)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Tile length (cm)	Tiles needed
15	285
30	144
45	97
60	73
75	58
90	49
120	37

How to read the result

The leftover tiles in the last box are useful spares for future repairs, because later batches may differ slightly in shade. Use about 10% waste for a simple straight layout, more for diagonal or herringbone patterns, small rooms with many cuts, or large-format tiles. Adhesive use depends mainly on the trowel notch size and whether you back-butter the tiles, so 4 kg/m² is only a mid-range guide.

Common mistakes

Forgetting the joint in the footprint; with small mosaics it changes the count noticeably.
Applying no waste to rooms with many corners, pipes or a diagonal layout.
Buying boxes from different production batches, which can show colour variation.

Keep in mind: Grout and adhesive figures are approximations. Real consumption depends on the product, trowel, tile back profile and substrate; follow the manufacturer's data and local standards, and use a qualified installer for wet rooms and heavy wall tiles.

Frequently asked questions

How much waste should I add?

About 10% for straight layouts and roughly 15% for diagonal or patterned layouts; large-format or fragile tiles may need more.

Does joint width change the number of tiles?

Slightly. Wider joints make each tile's footprint bigger, so fewer tiles are needed, but much more grout.

What joint width should I use?

It depends on the tile type and the manufacturer's recommendation; rectified tiles allow narrower joints than tiles with less regular edges.

Sources: EN 12004: Adhesives for ceramic tiles, CEN · EN 13888: Grout for ceramic tiles, CEN

Checked 8 Nov 2026. Typical coverage rates and standard formulas. Always check the product label and local building rules; buy 5–10% extra for waste.

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