How much screed do I need per square metre?

At 50 mm of traditional sand-cement screed, one square metre needs 0.05 m3 of material, about 100 kg. That's roughly 4.2 bags of 25 kg or 2.6 bags of 40 kg per m2 in raw material, rounded up when you reach the checkout. Liquid anhydrite is slightly heavier at about 105 kg per m2 for the same thickness.

How many bags of screed do I need for 20 m2?

For a 20 m2 floor at 70 mm thick traditional screed, you need about 1.4 m3 of material plus a 5% waste margin, so 1.47 m3. A 25 kg bag yields 0.012 m3 mixed, so that's 123 bags. At 40 kg per bag, you'd need 77 bags. Always round up to the nearest full bag; you can't split one.

What's the minimum screed thickness?

A traditional sand-cement screed needs at least 25 mm bonded, 50 mm unbonded, or 65 mm floating. A liquid anhydrite screed needs 25 mm bonded, 30 mm unbonded, or 35 mm floating. A bonded self-levelling top-up can go as thin as 3 mm, but it's not a substitute for a structural screed.

How long does screed take to dry?

A traditional sand-cement screed dries at roughly 1 mm per day up to 50 mm, then slows to about 2 days per extra millimetre. A 75 mm pour takes around 100 days. Liquid anhydrite dries slightly faster up to 40 mm. Temperature, humidity, and ventilation all push the time up or down, so a reliable rule is to test moisture with a calcium chloride or hood test before laying the finished floor.

What screed should I use over underfloor heating?

Both traditional sand-cement and liquid anhydrite work over UFH. Anhydrite is the popular choice in Germany and the Netherlands because it spreads evenly and needs less cover over the pipes (35 mm vs 45 mm for sand-cement). Always keep the minimum cover above the pipe top and let the screed dry fully before running the heating curve.

Screed Calculator

Find out exactly how much floor screed to buy. Bags, kilograms, drying time, and underfloor heating cover are all factored in.

What are you pouring?

Floor dimensions

Length

Width

Finished thickness

Traditional floors are typically 65 to 75 mm. Liquid screeds sit around 40 to 50 mm. A bonded self-levelling top-up is 3 to 15 mm.

Bag size

Bags to buy

123bags · 25 kg

Area covered: 20.00 m²
Volume (with waste): 1.470 m³
Total mass (mixed): 2940 kg
m2 per bag: 0.17 m²
Drying time: 90 days

Screed Calculator

How screed calculations work

How to measure your floor

Common mistakes to avoid

Frequently asked questions

Other Calculators

Tile Calculator

Paint Calculator

Flooring Calculator

Concrete Calculator

Loft Insulation Calculator

Wallpaper Calculator