Grout fills the gaps between tiles, so the amount depends on how much gap there is: small tiles and wide joints need several times more than large tiles with tight joints. This calculator works out the total joint volume from the tile size, joint width and joint depth, converts it to weight of dry grout, and rounds up to bags.
How it is calculated
- Joint length per square metre ≈ (tile length + tile width) ÷ (tile length × tile width). For 300 × 600 mm tile that is 5 m of joint per m².
- Joint volume = joint length × joint width × joint depth. Depth is the tile thickness, since grout fills the joint to the bottom.
- Weight = volume × 1.7 kg per litre, a typical figure for cement grout as mixed. Then add waste and round up to whole bags.
Example
12 m² of 300 × 600 mm porcelain, 9 mm thick, with 3 mm joints and 10% waste: 60 m of joint, 1.62 L of volume, about 3 kg of grout. One 5 kg bag covers it with plenty spare. The same 12 m² in 100 × 100 mm tile needs about 9 kg; in 50 × 50 mm mosaic, nearly 20 kg.
Choosing the grout
Unsanded (non-sanded) grout for joints up to about 3 mm (1/8 in) and for polished stone or glass that sanded grout would scratch. Sanded for joints from 3 to 12 mm. Wide-joint or sanded grout with coarse aggregate above that. Epoxy grout resists stains and chemicals and does not need sealing, at two to three times the price and with a shorter working time. Cement grouts in wet areas benefit from a penetrating sealer once cured.
Coverage on the bag
Manufacturers print coverage tables for standard tile sizes; if your figure disagrees with the bag, the bag is calibrated to their product density and is the safer guide. Most estimates come out within 10–15% of each other, which is what the waste allowance covers.
Frequently asked questions
How much grout do I need per square metre?
It depends entirely on tile size and joint width: about 0.25 kg/m² for 300 × 600 mm tile with 3 mm joints, 0.75 kg/m² for 100 × 100 mm, and 1.5 kg/m² or more for small mosaics. The comparison table shows several sizes for your area.
Sanded or unsanded grout?
Unsanded for joints up to 3 mm (1/8 in) and for surfaces that scratch; sanded for 3–12 mm. Sanded grout shrinks less and is stronger in wider joints.
How deep is a grout joint?
The full thickness of the tile, since grout fills from the substrate up. Ceramic wall tile is 6–8 mm, porcelain floor tile 9–10 mm, natural stone often 10–12 mm.
How much does a bag of grout cover?
A 10 kg bag does roughly 35 m² of large-format tile with narrow joints, or 6–8 m² of small mosaic. Use the calculator for your exact combination rather than a rule of thumb.
Sources
By Calcelate Team. Formula from the sources above.
- 2026-09-14 · Formula and texts checked