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Tile Grout Quantity Calculator

Buy the right amount of grout for your tiles instead of guessing in the shop.

How it is calculated

Area is in square metres; tile length, tile width, tile thickness and joint width are all in millimetres. Grout per square metre is kg/m² = (L + W) ÷ (L × W) × joint × thickness × 1.6, where 1.6 is the grout density in g/cm³. The engine assumes the joint is filled to the full tile thickness. The total is kg = kg/m² × area × 1.10, so a fixed 10 % is added for waste, spillage and uneven tile backs. The bag count is the total divided by 5 and rounded up to whole 5 kg bags. Every field must be above zero, and a joint wider than the shorter side of the tile is rejected as not being a tiling, so it shows no result. Real grouts differ in density, and the tiling layout matters, so always check the pack for its own coverage figure.

Worked example

The area is 20 m² of 300 × 300 mm tiles that are 8 mm thick with 3 mm joints. Per square metre, (300 + 300) ÷ (300 × 300) = 0.006667, and multiplying by 3 × 8 × 1.6 = 38.4 gives 0.256 kg/m². For 20 m² that is 5.12 kg, and adding 10 % waste gives 5.63 kg in total (5.632 before rounding). Divided by 5 kg per bag, 1.13 rounds up to 2 bags.

Try this example →

Common mistakes

  • Entering tile sizes in centimetres. The fields are in millimetres, so a 30 cm tile is 300; typing 30 makes the tile look tiny and the grout quantity far too large.
  • Entering the room area in square feet or including areas that will not be tiled, such as the space under a bath or kitchen units.
  • Typing the joint width in centimetres or as a fraction of the tile size. A normal joint is a few millimetres, so 3 is realistic and 0.3 is not; a joint wider than the tile gives no result.
  • Entering the adhesive-bed thickness instead of the tile thickness. The engine multiplies by the tile thickness you give, so a thicker figure overstates the grout.
  • Buying exactly the kilograms shown. The result already includes 10 % waste and bags are rounded up, but opened grout has a shelf life, so round to whole bags rather than topping up later.

About this calculator

Grout quantity depends on tile size, tile thickness and joint width — larger tiles need less grout per square meter because there are fewer joints, while thicker tiles or wider joints both increase the volume each joint holds. The standard trade formula multiplies the tiled area by the perimeter-to-area ratio of a single tile — (tile length plus tile width) divided by (tile length times tile width) — then by the joint width, the tile thickness and a grout density factor (roughly 1.6 for standard cementitious grout) to get the weight in kilograms.

Tilers and DIYers run this calculation before starting a job because buying grout by eyeballing the box size at the shop routinely leads to either running short mid-job with mismatched grout batches, or overbuying a product that has a shelf life and cannot simply be returned once opened.

The kilograms of grout needed come from your tiled area, tile size, tile thickness and joint width, so you can buy the right amount in one trip.

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