Grout Calculator
Work out exactly how much grout a tiled area needs — in kilograms and bags — from the tile size, joint width and joint depth. No guessing, no wasted bags.
Grout is the most commonly under-bought tiling material: a bag too few means a half-grouted floor and a second trip. The amount depends on tile size, joint width and depth — not just the area — so this calculator works from all four.
The formula uses the exact geometry of one tile plus its joints, and a standard cement-grout density of 1.6 kg per litre. Epoxy grouts are denser — allow about 10% more if you use epoxy.
Your results
Enter your measurements and press Calculate.
Quantities are rounded up to whole tiles, planks, boxes or bags, after the wastage allowance. Cost appears only when you enter a price.
Formula
All lengths are converted to a single unit before the calculation: 1 ft = 0.3048 m, 1 in = 25.4 mm, 1 ft² = 0.09290304 m², 1 yd² = 9 ft². Material quantities are rounded up — you cannot buy part of a tile, plank or bag.
How to use this calculator
- Measure the tiled area in square metres or square feet.
- Enter the tile size, the joint width and the joint depth.
- Enter your grout bag size — the calculator rounds up to whole bags.
- Add a price per bag if you want a cost estimate.
Worked example
| Area | 10 m² |
|---|---|
| Tile | 300 mm × 300 mm, 3 mm joint, 6 mm deep |
| Cell area | (303 × 303) = 91,809 mm²; grout area = 91,809 − 90,000 = 1,809 mm² |
| Litres per m² | (1,809 ÷ 91,809) × 6 = 0.118 L/m² |
| Kg per m² | 0.118 × 1.6 = 0.19 kg/m² |
| Total with 10% allowance | 0.19 × 10 × 1.10 = 2.08 kg → 1 bag of 5 kg |
Check it by hand: every step above uses the formula in the box. If your numbers match the example inputs but the calculator gives a different answer, please report it via the contact page.
Frequently asked questions
How much grout do I need per square metre?
It depends on tile size and joint width: large tiles with narrow joints need very little (about 0.2 kg/m² for 300 mm tiles with 3 mm joints), while small mosaics with wide joints can need 1 kg/m² or more. This calculator works it out exactly for your tiles.
What grout joint width should I use?
Wall tiles: 2–3 mm. Floor tiles: 3–5 mm. Large-format tiles (600 mm and over) need at least 3 mm, and often 5 mm, to absorb small size differences between tiles. Mosaics: 2 mm.
How deep should grout joints be?
Grout should fill about two-thirds of the tile thickness — for a 9 mm tile, about 6 mm deep. The joint must be raked out to a consistent depth before grouting, or the grout will crack.
Does this include a wastage allowance?
Yes — a 10% mixing and spillage allowance is built in, because grout is mixed in batches and some is always lost on the float and in wash-up. Buy whole bags only; the result is rounded up.
Related calculators
Estimates only. Results are for planning. Measure twice, confirm box coverage and tile sizes on the packaging you buy, and follow the manufacturer's instructions. See the disclaimer.