BuildSums

Screed calculator

Enter the floor area, screed depth and mix to see how many bags of cement and tonnes of sharp sand to order.

Your measurements

You’ll need the floor area and the depth of screed. If you’re screeding over insulation or underfloor heating, pick that option so we can check the depth. The boxes start with example figures, and the result updates as you type.

Length × width of the room
Or inches, like 3in

Result

Fill in the measurements to see what to order.

Figures checked 25 October 2026. See the sources, or report a problem.

How this is worked out

Volume is area × depth. To get materials we assume about 2,000kg of dry sand and cement per m³ of laid semi-dry screed, then split that by your mix ratio. That’s our working figure rather than a manufacturer’s, so add a little extra.

The depth check uses The Concrete Centre’s summary of BS 8204: 25mm minimum bonded, 50mm minimum unbonded, and 65mm as a common specification for floating screeds and screeds over heating pipes.

Worked example

A 20 m² extension floor, floating screed at 65mm, 4:1 mix: 20 × 0.065 = 1.3 m³. Dry material is 1.3 × 2,000 = 2,600kg. Cement is a fifth, 520kg, which is 21 bags of 25kg. Sand is 2,080kg, about 2.1 tonnes or three 850kg bulk bags.

Hand-mixed or delivered?

Up to about a cubic metre is doable with a mixer and a couple of people. Bigger floors are usually cheaper and flatter with a pumped or ready-mixed screed, and flowing calcium sulfate screeds can be laid thinner. Ask the supplier for their minimum depth over your insulation or pipes.

Questions people ask

How thick should floor screed be?

It depends how it’s laid. The Concrete Centre gives 25mm as the BS 8204-1 minimum for a bonded sand and cement screed, at least 50mm for unbonded (it suggests designing for 70mm), and floating screeds over insulation are commonly 65mm or more.

What mix is floor screed?

Sand and cement screed is usually 4:1 or 3:1 sharp sand to cement, mixed semi-dry so it holds together when squeezed. A 3:1 mix is stronger and uses more cement.

How many bags of cement per m³ of screed?

At 4:1, about 16 or 17 bags of 25kg per m³, based on 2,000kg of dry material per m³. At 3:1 it’s about 20 bags.

How long does screed take to dry?

A common rule of thumb is a day per millimetre for the first 40mm, then slower after that. Test before laying timber or vinyl floors, because trapped moisture causes failures.

Sources

Trade review pending. A named tradesperson will check this calculator, and their name and qualifications will appear here.

Figures last checked 25 October 2026. Read how we calculate and our disclaimer. Found a mistake? Tell us.