Tile Grout Calculator
Works out grout from the tile size, joint width and tile thickness. Those three together decide the answer, which is why coverage figures printed on a bag are only ever a rough guide.
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
The formula
kg/m² = (tile length + tile width) ÷ (tile length × tile width) × joint × thickness × 1.6
Each tile contributes a joint along two of its four edges, because the other two are shared with its neighbours. That is where the (L + W) ÷ (L × W) comes from. Thickness matters because the joint is as deep as the tile — a 20 mm stone slab needs twice the grout of a 10 mm ceramic at the same joint width.
What to watch out for
Three things drive grout quantity, and only one of them is the area:
- Tile size, inversely. Small tiles mean more joint per square metre. A mosaic can use ten times the grout of a large-format tile over the same floor.
- Tile thickness. The joint is as deep as the tile, so a 20 mm stone slab takes twice what a 10 mm ceramic does.
- Joint width. Directly proportional. Going from 2 mm to 4 mm doubles it.
Mix small batches. Grout starts going off in about 20 minutes, and re-tempering stiffened grout with more water gives a weak, patchy joint that discolours.
Frequently Asked Questions
How much grout do I need per square metre?
For 600 × 600 mm tiles 10 mm thick with 3 mm joints, about 0.16 kg/m². For 150 × 150 mm tiles at the same joint and thickness it is around 0.64 kg/m² — four times as much, because there is four times the joint.
Why do small tiles need more grout?
Because grout fills the joints, and smaller tiles mean more joints per square metre. Halving the tile size roughly doubles the length of joint in the same area.
Does tile thickness affect grout quantity?
Yes, directly. The joint is filled to the full depth of the tile, so a 20 mm stone tile uses twice the grout of a 10 mm ceramic at the same joint width.