How much tile adhesive do I need per m²?

It depends on the tile type and trowel size. For standard ceramic wall tiles, a 20kg bag covers 4-5 m². For larger format tiles or porcelain, coverage drops to around 3 m² per bag because you need a larger notched trowel (10-12mm) to ensure full bed coverage. Natural stone typically needs 2.5-3 m² per bag due to back-buttering requirements.

Should I use ready-mixed or powder tile adhesive?

Ready-mixed adhesive is convenient but only suitable for small ceramic wall tiles (up to about 200x200mm) in dry areas. For bathrooms, large format tiles, porcelain, or floor tiles, always use a flexible powder adhesive rated C2. Powder adhesive is stronger, more flexible, and suitable for wet areas. It is the professional standard in the UK.

Can I tile over existing tiles?

Yes, you can tile over existing tiles provided they are firmly bonded to the wall. Use a flexible powder adhesive rated C2 and roughen the existing tile surface with coarse sandpaper or a diamond pad. Apply a primer or slurry coat first. Check the wall can take the extra weight — two layers of tiles on plasterboard may be too heavy. Use our wall tile calculator (/tiling/wall-tile-calculator/) to work out total tile quantities.

What size notched trowel should I use?

For wall tiles up to 300mm, use a 6mm notched trowel. For tiles 300-600mm, use a 10mm or 12mm trowel. For large format floor tiles (600x600mm+), use a 12mm trowel and back-butter the tiles as well. The larger the notch, the more adhesive you use per m² — which is why coverage rates vary by tile size.

How long does tile adhesive take to set?

Standard flexible powder adhesive takes 24 hours before grouting. Rapid-set adhesive can be grouted after 3-4 hours. Ready-mixed adhesive takes 24-48 hours as it cures by evaporation. In cold conditions (below 5°C), allow extra time. Do not use rapid-set adhesive if you are a beginner — it leaves less working time for adjustments.

Tile Adhesive Calculator — How Many Bags Do I Need UK

Tile Adhesive Calculator — How Many Bags Do I Need?

Calculate the number of tile adhesive bags needed for your tiling project. Covers ceramic, porcelain, natural stone and mosaic tiles on all common substrates.

Total Area to Tile

Combined wall and/or floor area

Tile Type

Substrate

Surface the tiles will be fixed to

Adhesive Type

Include wastage allowance

Recommended for mixing and application losses

Wastage Percentage

10% is standard for tile adhesive

Price Per Bag (optional)

Enter your supplier price for a cost estimate

How We Calculate This

Our tile adhesive calculator divides your total tiling area by the coverage rate of the adhesive for your tile type. Coverage rates are based on manufacturer data from BAL, Weber, Mapei and Dunlop — the leading UK tile adhesive brands.

The formula

Bags needed = (Total area ÷ Coverage per bag) × Wastage factor

For example, tiling 12 m² with porcelain tiles (3 m² per bag): 12 ÷ 3 = 4 bags, plus 10% wastage = 5 bags of 20kg flexible adhesive.

Coverage rates we use

Ceramic small (<300mm): 4.5 m² per 20kg bag (6mm trowel)
Ceramic large (300mm+): 3.5 m² per 20kg bag (10mm trowel)
Porcelain: 3.0 m² per 20kg bag (10-12mm trowel, back-buttered)
Natural stone: 2.75 m² per 20kg bag (12mm trowel, back-buttered)
Mosaic: 5.0 m² per 20kg bag (4-6mm trowel, thin bed)

Substrate adjustments

Coverage can vary by substrate. Over-tiling existing tiles and tiling onto rough concrete typically uses 10-15% more adhesive than tiling onto smooth plasterboard or cement board. Our calculator adjusts for this automatically. All rates assume standard UK 20kg bags.

Frequently Asked Questions

Last updated: February 2026

All calculations are estimates. Verify with your supplier.

Tile Adhesive Calculator — How Many Bags Do I Need?

How We Calculate This

The formula

Coverage rates we use

Substrate adjustments

Frequently Asked Questions

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