Screed Calculator

Floor area, m²

Layer thickness, mm

Bag weight, kg

Advanced options

Mix density, kg/m³

Result

Volume, m³0.875
Mass of mix, kg1,575
Bags63
With 5% spare67
Water, l236.3
Days to dry42

Answers the material question and the schedule question

Mix volume, number of bags, water needed and how long the screed will take to dry at the thickness you choose.

Counting screed in bags beats counting it in cubic metres, because bags are what you buy and carry. One square metre at ten millimetres takes roughly 18 kg of dry mix — just under a bag.

The second answer matters as much: how long before you can lay flooring. The first 40 mm dry at about a week per centimetre, and anything above that at half that rate. A 70 mm screed is not ready for two months.

What this calculator shows

Volume and mass of mix, bag count and a figure with spare
How much water the mixing will need
An indicative drying time before flooring can go down

What to keep in mind

Cement-sand mix density is taken as 1800 kg/m³; gypsum-based self-levelling compounds are lighter, nearer 1500.
Drying time assumes around 20 °C and under 60 percent humidity. Cold or damp conditions stretch it out.

FAQs

What is the minimum screed thickness?

Thirty millimetres for cement-sand screed on a concrete base, forty where underfloor heating pipes are embedded. Self-levelling compounds go down from three.

How long before I can lay flooring?

Full strength takes 28 days for up to 40 mm. Laminate and tile go down once substrate moisture falls below about 4 percent — measure it rather than guess.

Does screed need reinforcing mesh?

Not necessarily up to 50 mm on a sound base. Over insulation, over timber, or beyond 50 mm it is essential or the screed will crack.

Why choose semi-dry screed?

Less water means less shrinkage and fewer cracks, and it takes foot traffic within a day. Mixing it by hand defeats the point — it only makes sense pumped.

Worked example

50 mm screed in a 17.5 m² room

Input: 17.5 m², 50 mm, 25 kg bags

Output: 0.875 m³, 1,575 kg, 63 bags, 42 days to dry

Note: Sixty-three bags is a tonne and a half to carry upstairs. Pumped semi-dry screed delivered on site is often cheaper once you count the labour.

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Screed Calculator

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