How Much Self-Levelling Compound Do I Need for a Room?

Fibre-reinforced compound at about 1.7kg per m² per mm, 20kg bags, 5% extra.

Page last reviewed 26 October 2026 by the UkToolCalc team

A 4 × 3m floor at 5mm average depth needs about 107kg of powder: 6 × 20kg bags. A 20kg bag covers about 2.3m² at 5mm.

Bags by room size and depth

Fibre-reinforced compound, 20kg bags, 5% extra.

Room	Area	Average depth	Powder	20kg bags
3 × 2 m	6 m²	3 mm	32 kg	2
4 × 3 m	12 m²	5 mm	107 kg	6
4.5 × 3.6 m	16.2 m²	5 mm	145 kg	8
5 × 4 m	20 m²	10 mm	357 kg	18

Powder (kg) = area (m²) × depth (mm) × 1.7 × 1.05 4 × 3m at 5mm: 12 × 5 × 1.7 × 1.05 = 107kg = 6 bags

The self-levelling compound calculator adds primer, water and edge strip. The self-levelling guide shows how to pour it without lines or bubbles.

How much does a 20kg bag of self-levelling compound cover?

At about 1.7kg per m² per mm, a 20kg bag covers about 3.9m² at 3mm, 2.3m² at 5mm and 1.2m² at 10mm.

How do I measure the average depth?

Lay a long straight edge across the floor in several places and measure the gaps under it. Take an average of the low spots, not the deepest one.

Do I need to prime before self-levelling?

Yes. Primer stops the floor sucking the water out of the compound and helps it bond. A 5L tub does most rooms.