Tile Adhesive Calculator — How Many Bags Do I Need?

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.