Floor Screed Calculator
How many bags of mix a floor of this area and thickness takes.
How it works
Screed is priced and sold by weight, so the useful number is kilograms rather than cubic metres. Consumption is quoted per square metre per centimetre of thickness — around 20 kg for most cement-sand mixes — which makes the total area times thickness times that rate.
The rate on the bag is what matters, and it varies by more than you would expect: lightweight and semi-dry mixes can be 30% off the figure used here. Check the packaging, and remember that an uneven base means the average thickness is greater than the thinnest point you measured.
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How the Floor Screed Calculator works
A floor screed calculator works out how much dry mix a floor of a given area and thickness takes, and converts the weight into bags. Consumption is expressed in kilograms per square metre for each centimetre of thickness — the way manufacturers quote it.
Why it is weighed rather than measured in volume
Screed is sold in bags, so the whole calculation is easier in weight. Typical consumption for a cement-sand mix is around 20 kg per square metre per centimetre of thickness. Multiply by area and by thickness in centimetres, divide by the bag weight, round up.
The figure on the bag matters more than any average. Lightweight mixes with expanded clay can be a third lower, semi-dry compounds higher. Check the packaging of the specific product before ordering.
Thickness: where the limits are
A bonded cement screed needs at least 30 mm. Thinner than that it cracks and debonds, because it never develops enough flexural strength. For a thinner layer you need a self-levelling compound, which is a different material with a different consumption rate.
The practical upper limit is around 70–80 mm, beyond which the load on the structure and the curing time both climb. Remember that average thickness always exceeds minimum thickness: the base is uneven and the screed makes up the difference. Measure from the highest point of the floor and add your layer above that.
FAQ
How many bags for a 5 cm screed?expand_more
At 20 kg per m² per centimetre that is 100 kg per square metre. In 25 kg bags, four bags per square metre; in 40 kg bags, two and a half. A 20 m² room works out at about 80 bags of 25 kg.
How long does screed take to dry?expand_more
Do I need reinforcing mesh?expand_more
From 50 mm and over a soft base, yes. Over a rigid slab at up to 40 mm, fibre in the mix is usually enough. Mesh does not change the screed consumption, but it does require at least 20 mm of cover above it.