Self-Levelling Compound Calculator UK

Self Levelling Compound Calculator UK

Work out exactly how many bags of self levelling compound you need before you start mixing. Enter your floor area and average depth and calculator gives you the total weight, bag count and estimated cost. Running out mid pour leaves a ridge in your floor, so getting the bag count right matters.

How to Calculate Self Levelling Compound

UK manufacturers rate coverage in kilograms per square metre per millimetre of depth. Most compounds sit between 1.66 and 1.8 kg/m²/mm, so the standard formula is:

Total kg = Area (m²) × Depth (mm) × 1.7

Then divide by your bag size, usually 20kg in the UK, and round up.

Working example: a 20 m² room needing 5mm of compound: 20 × 5 × 1.7 = 170kg. That is 8.5 bags of 20kg, so round up to 9 and add 10% waste to order 10 bags.

As a quick rule of thumb, one 20kg bag covers about 3 m² at 3mm or roughly 2.4 m² at 5mm. Coverage varies between brands, so check the datasheet for your specific product.

Bags Needed for Common Room Sizes

Based on a standard 20kg bag at 1.7 kg/m²/mm with 10% waste included:

Choosing the Right Depth

Self levelling compound is designed to smooth a floor rather than completely rebuild it. Use a straight edge or spirit level to find your low spots, measure the deepest dips and work to an average:

• 2 to 3mm for minor smoothing before vinyl, LVT or carpet
• 4 to 6mm for moderate levelling before tiling
• 8 to 10mm for more significant corrections, the limit for most standard products in one pour
• 15 to 50mm needs a specialist deep pour or fibre reinforced deep fill compound

If your subfloor needs more than 50mm of correction, a levelling screed is usually the better route than multiple compound pours.

Cost of Self Levelling Compound

Standard 20kg bags cost £10 to £15 from UK merchants. Rapid set versions run £15 to £20 and flexible or deep pour formulations £18 to £25. For our 20 m² example at 5mm, materials come to roughly £100 to £150.

If you hire a professional, labour adds £10 to £20 per m² or expect £20 to £35 per m² supply and fit. For floors over 20 m², professional installation is often worth it because the working time is short and a botched pour is expensive to grind off.

Application Tips That Save the Job

Prime first, always: Porous concrete sucks water out of the compound before it can flow and cure, causing weak spots and delamination. One coat of acrylic primer prevents this.

Do not overwater the mix: Extra water makes pouring easier but weakens the compound, leading to cracking and surface dusting. Stick to the ratio on the bag.

Work fast: The compound self levels within 10 to 20 minutes of pouring, so have every bag mixed and ready in sequence. A helper mixing while you pour makes larger rooms far easier.

Over timber floorboards: use a fibre reinforced compound, screw down any loose boards and seal gaps first or the liquid drains straight through.

Curing times: Rapid set products take foot traffic in 2 to 4 hours and tiling after 12 to 24 hours. Standard compounds need 24 to 48 hours. Cold rooms and high humidity stretch these times.