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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.
Combined wall and/or floor area
Recommended for mixing and application losses
10% is standard for tile adhesive
Enter your supplier price for a cost estimate
Powder bag weight (default 20kg). Coverage scales with weight. Ignored for ready-mixed (fixed 15kg tubs).
Indicative coverage multiplier when over-tiling smooth, flat existing tiles (default 0.95 — minor increase).
Indicative coverage multiplier for rough/porous concrete or sand-cement render (default 0.88 — uses more).
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How We Calculate This
Our tile adhesive calculator divides your total tiling area by the coverage rate of the adhesive for your tile type. The coverage rates below are typical UK trade figures, cross-checked against manufacturer consumption data (for example Mapei Keraflex Maxi S1 quotes 1.2 kg/m² per mm of bed). Actual coverage depends on your trowel size and how flat the substrate is, so always confirm against your adhesive’s data sheet. Our reference table on how much tile adhesive you need per square metre for every trowel sizeshows kg/m² rates from 4mm mosaic trowels up to 15mm large-format trowels.
The formula
Bags needed = (Total area ÷ Coverage per bag) × Wastage factor
For example, tiling 12 m² with porcelain tiles (3 m² per 20kg bag): 12 ÷ 3 = 4 bags, plus 10% wastage = 5 bags of 20kg flexible adhesive.
Coverage rates we use (per 20kg powder bag)
- Ceramic small (<300mm): 4.5 m² per 20kg bag (6mm trowel, ≈4.4 kg/m²)
- Ceramic large (300mm+): 3.5 m² per 20kg bag (10mm trowel, ≈5.7 kg/m²)
- Porcelain: 3.0 m² per 20kg bag (10-12mm trowel, back-buttered, ≈6.7 kg/m²)
- Natural stone: 2.75 m² per 20kg bag (12mm trowel, back-buttered, ≈7.3 kg/m²)
- Mosaic: 5.0 m² per 20kg bag (4-6mm trowel, thin bed, ≈4.0 kg/m²)
Because adhesive use is driven by kilograms per square metre, coverage scales with bag weight: a 10kg bag covers half the area of a 20kg bag, so the calculator scales the rates above by your chosen bag weight.
Ready-mixed adhesive
Ready-mixed paste is sold in tubs (for example weberfix Plus, supplied in a 15kg tub) and is only suitable for small ceramic wall tiles in light-duty areas. BAL White Star Plus is a similar ready-mixed wall adhesive but is sold by volume (2.5, 5 and 10 litre tubs). When you select ready-mixed, the calculator uses a tub coverage of about 5 m² per 15kg tub (≈2 kg/m² dry to ≈3.4 kg/m² wet, per the weberfix Plus data sheet) and reports tubs rather than bags. For porcelain, floors, large-format or wet areas use a C2 flexible powder adhesive instead.
Substrate adjustments
Coverage can vary with the substrate. These are indicative trade allowances, not fixed standard figures — rough, porous or uneven concrete and sand-cement render tend to consume a little more adhesive (default +14%), while over-tiling smooth, flat, well-bonded existing tiles makes only a small difference (default +5%). You can override both factors in Advanced Options. Follow your adhesive manufacturer’s coverage notes and BS 5385 workmanship guidance for the exact bed required.
Working figures for this are collected in our Adhesive Coverage Rates reference table.
Frequently Asked Questions
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.
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.
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 to work out total tile quantities.
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.
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.
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Last updated: February 2026
Verified against UK standards · estimates only, confirm with your supplier.