Grout Calculator

Grout use depends on tile size and joint width more than on area alone. Small tiles and wide joints use far more.

Worked example

300 x 300 mm tiles, 3 mm gaps, 10 mm joint depth, 10 m². Each tile cell is 303 x 303 mm, so the grout fraction = 1 - (300 x 300) / (303 x 303) = 1.97% of the area. Joint volume = 10 m² x 1.97% x 10 mm = 1.97 L. At about 1.6 kg per litre: 3.15 kg, so one 5 kg bag covers the job with the waste allowance included.

How it works

Grout fraction of the surface = 1 - (tile length x tile width) / ((tile length + gap) x (tile width + gap)). Joint volume in litres = area (m²) x grout fraction x joint depth (mm). Weight = volume x density, using about 1.6 kg per litre of joint volume (approximate); actual density varies by product, so check the coverage chart on the bag. Bags include a 10% allowance for mixing loss and cleanup.

FAQ

What should I use for joint depth?

Use the tile thickness as a starting point. Joints are rarely filled to the full tile depth, so the estimate is conservative; trowel notches and uneven thinset beds can also change real usage.

Does grout colour or type change the amount?

The volume is the same, but sanded and unsanded grouts differ in density and in the joint widths they suit. Unsanded suits narrow joints (about 3 mm and under) and polished tile; sanded suits wider joints. Follow the product label.

Estimates only. This calculator gives planning estimates, not professional advice. Confirm coverage on the grout manufacturer's chart before buying.