United Kingdom · Materials & DIY
Grout Calculator
Change the pack size
Enter the tiled area and the coverage rate for your tile and joint size. The calculator returns kilograms and bags, and the table below explains why the tile size matters more than the area.
How much grout do I need per square metre?
It depends far more on tile size than on area. Large 600 by 600 mm tiles with 3 mm joints use roughly 0.3 kg per square metre. Small 100 by 100 mm tiles with the same joints use about 1.8 kg — six times as much, because there is six times as much joint length in each square metre.
How to use this calculator
- Enter the tiled areaThe surface being grouted, not the room. Walls and floors are usually different tile sizes and should be calculated separately.
- Get the coverage rate from your tile sizeThis is the input that matters. The table below gives typical figures; the bag will give the manufacturer's own, which is more reliable.
- Keep the waste allowance high15% is realistic for grout, higher than most materials. It gets wiped away, left in the bucket and wasted when you mix a batch too big to use before it goes off.
- Buy one colour batchGrout colour varies between production batches. Running short and buying more later can leave a visible difference across a floor.
How the calculation works
Grout fills the joints, so the quantity depends on the total joint volume in a square metre — and that is driven by how many tiles fit in that square metre, not by the area itself.
A square metre of 600 by 600 mm tiles contains under three tiles and about 3.3 metres of joint. A square metre of 100 by 100 mm tiles contains a hundred tiles and roughly 20 metres of joint. Same area, six times the grout.
Joint width and depth then scale it linearly. Doubling the joint width doubles the grout. Tile thickness sets the depth, so a 20 mm porcelain paver uses twice the grout of a 10 mm ceramic at the same joint width.
This is why mosaic sheets consume grout at a rate that surprises people — a small bathroom floor in 25 mm mosaic can use more grout than a large room in format tiles.
coverage ≈ ((tile length + tile width) ÷ (tile length × tile width)) × joint width × joint depth × grout densityGrout coverage by tile size
| Tile size (mm) | 3 mm joint | 5 mm joint | Joint length per m² |
|---|---|---|---|
| 600 × 600 | ≈ 0.3 kg/m² | ≈ 0.5 kg/m² | 3.3 m |
| 300 × 600 | ≈ 0.45 kg/m² | ≈ 0.75 kg/m² | 5.0 m |
| 300 × 300 | ≈ 0.5 kg/m² | ≈ 0.9 kg/m² | 6.7 m |
| 200 × 200 | ≈ 0.8 kg/m² | ≈ 1.3 kg/m² | 10.0 m |
| 100 × 100 | ≈ 1.8 kg/m² | ≈ 3.0 kg/m² | 20.0 m |
| 25 × 25 mosaic | ≈ 5.5 kg/m² | ≈ 9.0 kg/m² | 80.0 m |
These assume a 10 mm tile thickness. A thicker tile increases the joint depth and the grout proportionally — a 20 mm outdoor porcelain paver uses roughly double the figures above.
Worked example: a bathroom
A bathroom with 7.2 m² of wall in 300 by 600 mm tiles at 3 mm joints, plus 2 m² of floor in 300 by 300 mm at 3 mm.
The walls at 0.45 kg/m² need 3.24 kg. The floor at 0.5 kg/m² needs 1 kg. Adding 15% waste to each gives 3.73 kg and 1.15 kg — 4.88 kg in total, so a single 5 kg bag covers it with almost nothing spare.
Now swap the floor for 25 mm mosaic. Two square metres at 5.5 kg/m² is 11 kg before waste, 12.65 kg after. The floor alone now needs three 5 kg bags, and the total more than triples for a fifth of the area.
That is the practical lesson: when a mosaic or small-format tile is specified, recalculate the grout rather than assuming the previous figure still applies.
Choosing the right grout
Cement-based grout is the default and comes in sanded and unsanded forms. Unsanded is for joints under about 3 mm, because sand will not pack into a narrow joint. Sanded is for wider joints, where the sand resists shrinkage and cracking. Using unsanded grout in a wide joint produces cracking; using sanded grout on a polished or soft-glazed tile can scratch the surface.
Epoxy grout is a different product entirely. It is stain-resistant, chemically resistant and effectively waterproof, which makes it the right answer in wet rooms, commercial kitchens and anywhere subject to staining. It costs several times more, has a short working time, and is genuinely difficult to clean off tile faces if you fall behind. Most people who try it for the first time on a large floor regret the choice.
Flexible grout is worth specifying over underfloor heating and on any substrate that moves. Standard cement grout in a heated floor cracks along the joints within a couple of heating seasons.
One thing grout is not, in any form, is a substitute for movement joints or silicone. Internal corners, wall-to-floor junctions and perimeters need a flexible sealant, because rigid grout in a corner will crack the moment the building moves.
Grout colour shifts as it cures, usually drying lighter than it looks when wet. Judging the colour from a wet joint leads to disappointment. If the colour matters, grout a small offcut area first and let it cure fully.
Assumptions and limitations
- Coverage rates assume a 10 mm tile thickness — thicker tiles use proportionally more
- Assumes uniform joint width across the whole area
- Does not account for bevelled or rectified edges, which change the effective joint volume
- Excludes silicone for corners and perimeters, which is a separate requirement
- Brand coverage varies; the manufacturer's figure for the specific product is more reliable
- Epoxy grouts have different coverage rates entirely and should use the manufacturer's data
Questions people ask about this in United Kingdom
How much grout do I need per square metre?
It depends on the tile size far more than the area. Large 600 by 600 mm tiles at 3 mm joints use about 0.3 kg per square metre; 100 by 100 mm tiles use around 1.8 kg, and 25 mm mosaic around 5.5 kg.
The reason is joint length: a square metre of mosaic contains roughly 80 metres of joint against 3.3 metres for large format.
Should I use sanded or unsanded grout?
Unsanded for joints under about 3 mm, because sand will not pack into a narrow joint. Sanded for wider joints, where the sand resists shrinkage cracking. Sanded grout can scratch polished or soft-glazed tiles, so test on an offcut first.
Is epoxy grout worth it?
In wet rooms, commercial kitchens and anywhere subject to staining, yes — it is effectively waterproof and stain-resistant. It costs several times more, has a short working time and is very difficult to remove from tile faces once it starts to set, which makes a large first-time floor a poor place to learn.
Do I need flexible grout over underfloor heating?
Yes. A heated floor expands and contracts with every cycle, and standard cement grout cracks along the joints within a couple of seasons. Flexible grout and a flexible adhesive are both the correct specification there.
Why did my grout dry a different colour?
Cement grout almost always dries lighter than it looks when wet, and inconsistent mixing or uneven drying makes it patchy. Mixing every batch to the same water ratio and grouting a whole area in one session are the two things that most affect the result.
Can I grout right into the corners?
No. Internal corners, wall-to-floor junctions and perimeters need flexible silicone rather than rigid grout, because those are exactly the places the building moves. Grout in a corner cracks, and the crack lets water through.
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Method, source and review date
- How it is worked out
- Coverage by joint volume, derived from tile size, joint width and joint depth
- Formula used
grout (kg) = area (m²) × coverage rate for the tile and joint size- Basis
- Standard mix ratios and coverage rates, editable on the page
- Last reviewed
- Confidence
- Medium
Coverage varies between grout brands and rises on uneven or bevelled tiles. Use the manufacturer's stated coverage for the specific product where you have it.
Spotted a figure that has moved, or a formula you can show is wrong? Tell us — send a correction. Fixes to rates and formulas are treated as urgent.
Disclaimer
Quantities are an estimate for planning and ordering. Site conditions, wastage, cuts and delivery minimums all change what you actually need — always confirm with your supplier or the person laying the material before ordering.