Grout Calculator - How Much Grout Do You Need? (UK)
Pop in your tile size, joint width and the area you're tiling, and this works out how much grout to buy using the standard tiling formula.
Interested? Then → Quotato for Tilers · More advice on the Blog & Chips guides.
How to use this calculator
Enter the length, width and thickness of a single tile in millimetres, then the joint width and the total area you're tiling. We work out the kilos of grout using the industry-standard formula, rounded up to whole kilos.
How we calculate this
- We use the standard UK formula: grout (kg/m²) = ((L + W) ÷ (L × W)) × joint width × tile thickness × 1.6.
- L and W are tile length and width in mm; joint width and thickness in mm; 1.6 is the typical density of dry grout.
- Total grout (kg) = grout per m² × area in m².
- We round up to the next whole kilogram, as grout is sold in fixed tub and bag sizes.
Worked example
For 300 × 300 mm tiles, 8 mm thick, 3 mm joint: ((300 + 300) ÷ (300 × 300)) × 3 × 8 × 1.6 = 0.256 kg/m². Across 10 m² that's 2.56 kg, so order 3 kg.
UK notes & gotchas
- Grout is usually sold in 3 kg, 5 kg, 10 kg or 20 kg tubs and bags - round up to the next size.
- Smaller tiles and mosaics have far more joints per m², so use noticeably more grout.
- Wider joints, deeper tiles and uneven backs all increase usage - buy a little extra if irregular.
FAQ
What is the 1.6 figure?
The approximate bulk density of dry grout in kg per litre. It converts the joint volume you're filling into a weight of grout.
Does joint width make a big difference?
Yes - usage is proportional to joint width, so a 5 mm joint uses about two-thirds more than a 3 mm joint on the same tiles.
Why round up to whole kilos?
Grout comes in fixed sizes, and it's better to have a little spare than run out mid-job.
Does this work for wall and floor tiles?
Yes - just enter the real tile dimensions and joint width. Floor tiles are often thicker, which the thickness input covers.