Self-Levelling Compound Calculator — How Many Bags Do I Need?

Our self-levelling compound calculator works by multiplying your floor area by the application depth and the compound's coverage rate (kg per m² per mm). We then divide by 25kg to give you the number of standard bags needed.

The formula

Bags needed = (Area × Depth × Coverage rate) ÷ 25kg

For example, a 20 m² floor at 3mm depth using standard compound (1.6 kg/m²/mm): 20 × 3 × 1.6 = 96 kg ÷ 25 = 4 bags (before wastage).

Coverage rates we use

• Standard compound: 1.6 kg per m² per mm — a 25kg bag covers ~5.2 m² at 3mm (Mapei Ultraplan Eco)
• Fibre-reinforced: 1.7 kg per m² per mm — a 25kg bag covers ~4.9 m² at 3mm (Mapei Ultraplan Maxi)
• Fast-set: 1.6 kg per m² per mm — a 25kg bag covers ~5.2 m² at 3mm (Mapei Ultraplan Fast Track)

Primer calculation

Primer is calculated at a conservative 1 litre per 5 m² of floor area. Actual primer coverage varies widely with subfloor absorbency and dilution: diluted acrylic primer on absorbent concrete or screed can reach ~20 m² per litre (Setcrete Acrylic Primer: 50 m² from a 2.5 L bottle diluted), while neat primer on a non-absorbent surface is closer to ~10 m² per litre (~25 m² from 2.5 L). Our default 5 m²/L errs safe so you don't run short — adjust the “Primer Coverage” field in Advanced Options to match your product's data sheet. Rates here reflect typical UK products from Setcrete, Weber, Mapei and Ardex ranges.