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Grout Calculator — How Much Grout Do I Need?
Calculate exactly how much grout you need based on tile size, joint width and tile thickness. Uses accurate volume-based calculations for all standard UK tile sizes.
Total area of tiling to grout
Standard wall tiles: 2mm, floor tiles: 3-5mm
Typical wall tile: 8mm, floor tile: 9-10mm
Recommended for mixing and cleaning losses
10% is standard for grout
Enter your supplier price for a cost estimate
Density of cementitious grout (default 1800 kg/m³)
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How We Calculate This
Our grout calculator uses a volume-based formula to determine exactly how much grout you need. Rather than rough estimates, we calculate the actual volume of grout joints per square metre based on your tile dimensions, joint width and tile thickness.
The formula
Grout (kg) = Area × Joint length per m² × Joint width × Tile thickness × Grout density
Joint length per m² is calculated as: (1000 ÷ tile width) + (1000 ÷ tile height), giving the total linear metres of grout joint in every square metre of tiling.
Worked example
For 10 m² of 300×600mm tiles with 2mm joints and 8mm tile thickness:
- Joint length per m² = (1/0.3) + (1/0.6) = 3.33 + 1.67 = 5.0 m/m²
- Grout volume per m² = 5.0 × 0.002 × 0.008 = 0.00008 m³
- Grout weight per m² = 0.00008 × 1800 = 0.144 kg
- Total grout = 10 × 0.144 = 1.44 kg, so 1 × 2.5kg bag or 1 × 5kg bag
Grout density
We use a grout density of 1,800 kg/m³ which is the industry average for cementitious grout. Coverage rates align with manufacturer data from BAL, Weber, Mapei and Dunlop. We recommend adding 10% wastage for mixing losses and cleaning.
Working figures for this are collected in our UK Grout Coverage Rates by Tile Size reference table.
Frequently Asked Questions
It varies hugely depending on tile size, joint width and tile thickness. Small metro tiles (100x200mm) with 2mm joints and 8mm thickness need roughly 0.4–0.5kg per m², while large 600x600mm floor tiles with 3mm joints (10mm thick) need only around 0.15–0.2kg per m² — fewer joints per square metre means far less grout, even with wider joints. Our calculator gives you the precise amount based on your specific tile and joint dimensions.
BS 5385-1:2018 sets a size-dependent minimum joint width: tiles with a facial area under 0.1 m² and no side over 600mm need a minimum of 2mm, while tiles from 0.1 m² up to 1 m² (no side over 1200mm) need a minimum of 3mm. So small metro tiles (100x200mm) suit a 2mm joint, but large-format tiles such as 300x600mm or 600x600mm fall in the 3mm-minimum band — a 2mm joint on those sizes is below standard. Floor tiles typically use 3-5mm joints to allow for slight size variations. Always check the grout manufacturer's stated joint range on the bag.
For joints up to 3mm wide, use unsanded (fine) grout — this is standard for most UK wall tiling. For joints wider than 3mm (common on floor tiles and natural stone), use sanded grout which resists cracking in wider joints. Most UK grout brands like BAL, Weber and Mapei clearly state the recommended joint width range on the bag.
Wait at least 24 hours after tiling with standard adhesive before grouting. With rapid-set adhesive, you can grout after 3-4 hours. The adhesive must be fully set before grouting — otherwise the pressure of grouting can shift tiles. In cold or damp conditions, allow extra drying time.
Yes, it is recommended to seal grout in bathrooms and wet areas with a grout sealer after it has fully cured (usually 72 hours). Sealing prevents water absorption, staining and mould growth. Alternatively, use an epoxy grout which does not need sealing — though it is harder to apply and more expensive. Silicone sealant (not grout) should be used in all internal corners and where tiles meet sanitaryware. For wet room installations, see our Wet Room Tanking Calculator for waterproofing requirements.
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Last updated: February 2026
Verified against UK standards · estimates only, confirm with your supplier.