Screed Calculator (UK)
Work out exactly how much material your floor screed needs before you order a grain of sand. This UK screed calculator handles both traditional sand and cement screed and modern liquid (flowing) screed. Enter your floor area and depth, pick your mix ratio, and it returns the volume of screed plus the cement bags and sharp sand you'll need, with wastage built in. Everything is metric and worked to UK practice under BS 8204-1. It's free, works on your phone on site, and there's a full worked example below.
How to use this screed calculator
- 1.Measure the floor in metres.
- 2.Choose your screed type and depth.
- 3.Pick the mix ratio for sand & cement.
- 4.Read off the cement bags and sand tonnage, and order with the wastage included.
Most groundworkers add 10% for waste, spillage and the odd deep patch where the sub-base dips.
Screed thickness — UK minimums
Minimum screed thickness depends on how it's bonded to the base, under BS 8204-1 (in-situ cement:sand levelling screeds). A floating screed for a domestic room is usually 65 mm minimum unreinforced, and 75 mm is the safe, common default — which is why this tool defaults to 75 mm.
| Screed type | Typical minimum depth | Common use |
|---|---|---|
| Bonded (glued to a clean concrete base) | 25–40 mm | Thin build-ups, patch repairs |
| Unbonded (on a membrane/DPM) | 50 mm | Over slabs with damp-proofing |
| Floating (on insulation) | 65–75 mm | Domestic floors, most new builds |
| Floating with underfloor heating | 65–75 mm over pipes | UFH systems |
Screed mix ratio — which to pick
A 1:4 (cement : sharp sand) mix is the standard general-purpose floor screed and the right default for most jobs. Go 1:3 for a stronger, higher-wear screed or thinner bonded sections. 1:5 is weaker and used less often. Always use sharp sand, not building (soft) sand — soft sand makes a weak, crack-prone screed.
Worked example: a 25 m² kitchen-diner floor
Say you're screeding a 25 m² kitchen-diner in a Manchester semi at 75 mm over insulation, using a 1:4 mix with 10% wastage.
- Compacted volume: 25 × 0.075 = 1.875 m³
- Add 10% wastage: 2.06 m³ of screed
- Dry materials (× 1.30): 2.68 m³, split 1:4
- Cement: ≈ 0.54 m³ → about 31 × 25 kg bags
- Sharp sand: ≈ 2.15 m³ → about 3.4 tonnes (≈ 5 bulk bags)
At 2026 builders'-merchant prices (roughly £5.50 a 25 kg bag of cement and £52 a bulk bag of sharp sand), that's about £170 in cement and £260 in sand, so budget around £430 in materials before mixer hire and labour. A screeding gang would typically lay this in half a day.
A point most calculators skip
Bagged "ready screed" looks convenient, but the maths kills it on anything but small patches. That same 25 m² floor would need roughly 165 × 25 kg bags of pre-mixed screed. Mixing sharp sand and cement yourself, or ordering a pump-mix for larger areas, is far cheaper per m². Pre-bagged only earns its place on repairs and tight spaces where a mixer won't fit.
Thickness, base build-up and finishes
Going much beyond ~100 mm generally means you're better off with a structural layer — see our Concrete Volume Calculator. Below the screed, most floors sit on a sub-base and slab — use our concrete slab bag calculator for the base beneath the screed, and check the sub-base and gravel build-up underneath that. Once the screed is cured, most floors get a finish laid on top — size the job with our tile calculator.
Frequently asked questions
Related tools
- Concrete Volume Calculator — calculate concrete volume for slabs, footings, and columns
- Concrete Slab Bag Calculator — how many bags of concrete for a slab
- Tile Calculator — how many tiles for the finish on top of your screed
- Gravel Under Concrete Slab Calculator — sub-base and gravel beneath the slab
Disclaimer: This calculator gives material estimates for planning only. Final quantities depend on your sub-base, compaction and site conditions. For structural or specification-critical work, confirm depths and mixes against BS 8204-1 and your project's drawings, and consult a qualified professional.