How Grout and Adhesive Calculator Works

Enter your area, tile size, and whether you are tiling walls or floors. The calculator returns adhesive in 20kg bags based on the coverage rate for your tile format, trowel size, and grout in kilograms from your tile and joint dimensions, each with wastage included.

The reference point worth knowing before any merchant trip: a standard 10 m² area in 300 × 300mm tiles typically needs around 2 bags of 20kg adhesive and roughly 5kg of grout. Adhesive is always the bigger line on the order, usually by a factor of five or more by weight, which surprises first-time tilers who budget the two equally. For fine-tuning only the grout weight, you can use our dedicated Grout Calculator UK.

Adhesive Coverage: Numbers That Matter

Adhesive consumption is set by the trowel, because notch size dictates the bed depth. Wall tiles with a 6mm notched trowel yield 4 to 5 m² per 20kg bag, standard floor tiles with an 8 to 10mm notch yield 3 to 4 m² per bag, and large format tiles over 600mm with a 10 to 12mm notch plus back-buttering yield around 3 m² per bag.

Two rules protect the job more than any quantity: floors always take cementitious powder adhesive, never ready-mixed tub adhesive, which lacks strength for foot traffic and never fully cures under large tiles. Movement needs flexibility: underfloor heating, wet rooms, and timber substrates call for an S1 flexible adhesive, stepping to S2 under very large formats. Large tiles also need back-buttering, a thin skim on the tile back as well as the combed bed, to eliminate hollow voids that cause corner cracks later.

Grout: Enough, in One Batch

Grout quantities come from joint dimensions rather than area alone, which is why a mosaic wall drinks grout while large format tiles sip it: more joints per square metre means more grout. As working figures, most domestic tiling uses 0.2 to 0.5kg per m², with 300 × 300mm floor tiles at 3mm joints sitting near the bottom of that range and mosaics several times higher.

Whichever route you take, buy all grout for a job at once and from one batch, because grout colour varies subtly between batches and a mid-wall colour change is permanent. Joint width also picks the grout type: fine unsanded grout for joints under 3mm, standard sanded grout above, and epoxy where showers and worktops justify its stain-proof, seal-free finish at a higher price and difficulty.

Sequencing the Job

The materials interact with time. Adhesive must cure before grouting starts, which means waiting at least 24 hours after the last tile goes on; grouting too early traps moisture and weakens both. Rake spacers and any adhesive squeeze-out from joints while the adhesive is still green, because hardened adhesive in a joint steals space grout needs and shows as a thin, weak line later. Fresh plaster wants four weeks of curing and a proper tile primer (never PVA), and floors should be flat within 3mm over 3m before a single tile is laid.

Worked Example

A 12 m² bathroom: 8 m² of walls in 300 × 600mm tiles and 4 m² of floor in 600 × 600mm porcelain:

• Wall adhesive at 4.5 m² per bag: 2 bags of 20kg.
• Floor adhesive at 3 m² per bag with back-buttering: 2 bags of flexible S1.
• Wall grout at roughly 0.3kg per m²: 2.4kg.
• Floor grout at roughly 0.25kg per m²: 1kg.
• Order: 4 bags of adhesive and one 5kg bag of grout covers both with a sensible spare.

The single 5kg grout bag covering the whole room is typical, and any leftover keeps for future repairs if stored sealed.