Screed Mix Ratio: How Much Sand and Cement for a Floor Screed (UK Guide)
Published 2026-07-10 · Browse all tools
Get the screed mix ratio wrong and you'll know about it within a year. Too little cement and the floor turns to dust under the tiles. Too much and it shrinks, curls at the edges and cracks. The good news is that floor screed is one of the simpler mixes on site once you know the ratio, the right sand, and how to turn a room's dimensions into bags and tonnes. This guide covers all three, the UK way, in metric, with a worked example you can copy.
If you'd rather skip the maths, the screed calculator does the sand and cement for you. But it helps to understand what it's doing.
Use the Screed Calculator hereThe standard screed mix ratio
For a general-purpose floor screed, the ratio is 1:4 — one part cement to four parts sharp sand, by volume. That's the default for the vast majority of domestic and light commercial floors in the UK, and it's the mix most screeding gangs reach for without thinking.
You'll see three ratios in practice:
- 1:3 — a stronger, higher-cement mix. Use it for thin bonded screeds, heavier point loads, or where a floor takes a hammering. It costs more in cement and is slightly more prone to shrinkage if it's laid too wet.
- 1:4 — the standard. The right balance of strength, workability and cost for most floors. If you're not sure, this is your answer.
- 1:5 — a weaker, sandier mix. Occasionally specified for cost reasons on lightly loaded floors, but it has less margin for error. Most trades avoid going leaner than 1:4.5.
Sharp sand, not building sand — this matters more than the ratio
This is the mistake that ruins more screeds than any ratio error. Screed must be made with sharp sand (also called grit sand or concreting sand), never soft building sand.
Soft sand is fine, rounded and made for bricklaying mortar, where you want a buttery, workable mix. Put it in a floor screed and you get a weak, dusty surface that never reaches proper strength and breaks up under foot. Sharp sand has larger, angular grains that lock together and give the screed its backbone.
Ask the merchant for sharp sand or concreting sand by name. At Travis Perkins, Jewson or Selco it's sold loose by the tonne or in bulk bags. If a bag says "building sand" or "plastering sand", it's the wrong stuff for a floor.
How much sand and cement do you actually need?
Here's the method the calculator uses, so you can check it by hand.
Step 1 — screed volume. Area (m²) × (thickness in mm ÷ 1000) = volume in m³.
Step 2 — add wastage. Most groundworkers add around 10% for spillage, a dip in the sub-base, and the odd deep patch.
Step 3 — allow for compaction. Loose dry sand and cement takes up more space than the finished, compacted screed. Multiply the volume by about 1.3 to get the dry materials you need to buy.
Step 4 — split by the ratio. For 1:4, that dry volume divides into 1 part cement and 4 parts sand (five parts total).
Step 5 — convert to bags and tonnes. Cement weighs about 1,440 kg per m³, so a cubic metre is roughly 58 × 25 kg bags. Sharp sand runs about 1.6 tonnes per m³.
Worked example: a 25 m² kitchen-diner
Take a real job. You're screeding a 25 m² kitchen-diner in a Leeds semi, over insulation, at 75 mm — the standard floating-screed depth — using a 1:4 mix and 10% wastage.
Compacted volume: 25 × 0.075 = 1.875 m³. With 10% wastage: 2.06 m³ of screed. Dry materials (× 1.3): about 2.68 m³, split 1:4. Cement: roughly 0.54 m³ → about 31 × 25 kg bags. Sharp sand: roughly 2.15 m³ → about 3.4 tonnes (around 5 bulk bags).
At 2026 builders'-merchant prices — call it £5.50 for a 25 kg bag of cement and £52 for a bulk bag of sharp sand — that's about £170 in cement and £260 in sand. Budget around £430 in materials before mixer hire and labour. A two- or three-person gang would usually lay this in half a day.
Traditional screed vs liquid screed
The 1:4 ratio is for traditional sand and cement screed — mixed on site, laid and floated by hand. It's cheap, flexible and forgiving of odd shapes, but it's slow and only as flat as the person laying it.
Liquid (flowing) screed is a different animal. It's pumped, self-levelling, and can go thinner — often 30–40 mm bonded. You don't mix it by ratio yourself; it's supplied ready to pour, usually anhydrite (calcium sulfate) or a cementitious flowing screed from a supplier like Tarmac or a specialist local pump-mix firm. For sizing liquid screed you only need volume, not a ratio — the screed calculator has a separate mode for it.
A few things that catch people out
- Don't over-water the mix. A screed should be "moist enough to ball in the hand but not wet". A sloppy screed shrinks and cracks as it dries.
- Curing beats speed. Cover a fresh screed with polythene for a few days so it dries slowly and evenly.
- Drying time is long. A rough rule is a day per millimetre for the first 50 mm, so a 75 mm screed can take well over a month to be dry enough to tile over.
- Add fibres or mesh for thin or heated screeds. Polypropylene fibres in the mix help control shrinkage cracks on floating and UFH screeds.