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Screed Calculator
Ordering sand and cement for a floor screed by eye is how you end up a barrow short on lay day — or with half a tonne of sharp sand going hard in the rain. Enter the floor area and the screed depth, and get an honest volume with the sand and cement to match.
Mix ratio: 4:1 sand:cement by volume
Every figure here is an estimate, rounded up. Materials are worked out from the finished screed volume plus a dry-materials allowance — actual quantities vary with the sand's moisture, how tightly it's compacted and site conditions. For big areas, a ready-mixed floor screed delivered by pump is often quicker and more consistent than mixing on site — worth pricing up.
How much screed do I need?
Start with the volume: multiply the floor area by the screed depth. A 20 m² floor at 75mm needs 20 × 0.075 = 1.5 m³ of laid screed, and it's sensible to add around 10% for wastage and compaction. From that volume you can work out materials — for a traditional 4:1 mix, roughly 1.6 tonnes of sharp sand and about sixteen 25kg bags of cement per cubic metre of finished screed. This calculator does the maths for you and rounds up so you're not left short on the day.
What's the mix for a sand and cement screed?
A traditional bonded floor screed is a 4:1 mix — four parts sharp (grit) sand to one part cement, measured by volume, mixed with just enough water to reach a firm, "just-holds-together" consistency. Screed is a much drier mix than concrete, which is why it's rammed and trowelled rather than poured. Where extra strength is needed you can go to a richer 3:1 mix. Always use sharp sand rather than soft building sand, and keep the water down — a wet screed is a weak screed.
How thick should a floor screed be?
For a bonded screed laid onto a prepared concrete base, around 50–75mm is typical. An unbonded screed (laid over a damp-proof membrane) usually wants at least 65–75mm, and a floating screed over insulation needs more again — commonly 65–75mm for domestic loads and up to 100mm or more where there's underfloor heating or heavier use. Going too thin risks cracking and curling; too thick wastes material and slows drying. If you're unsure for your build-up, check with your screeder or the insulation manufacturer.
Tiling on top once the screed's cured?
A screed needs time to cure before you tile on it — typically around a day per millimetre of thickness for the first stage, longer to be fully dry. When it's ready, our Tile, Adhesive & Grout Calculator works out the tiles, adhesive and grout for the finished floor.
Does this tool store my details?
No. There's no sign-up and nothing to submit — every calculation runs entirely in your browser as you type. Nothing you enter is uploaded, saved or sent anywhere, so you can use it as many times as you like without leaving a trace.
Please note: this tool gives a guide or estimate only. It may not be 100% accurate and is not professional advice — always check the figures before you rely on them. Nothing you enter is uploaded — the calculation runs entirely in your browser.
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