Screed Calculator UK: Floor Screed, Liquid Screed, Cost and Drying Time
Choose your screed and enter the floor dimensions. This screed calculator then estimates the materials, the typical installation price and the drying time. The first tab covers traditional sand and cement screed in tonnes and bags. The second estimates liquid screed in cubic metres, and the third calculates levelling compound.
More free UK building calculators
Screed sits between the concrete slab and the finished floor. These calculators cover the layers above and below it.
Sharp, building and kiln-dried sand, plus sand and cement mixes.
Cubic metres, bags, cement and ballast for slabs and footings.
Tiles per m², boxes and wastage for floors and walls.
Adhesive per m² and 20 kg bags by trowel notch.
Grout per m² from tile size, joint width and depth.
Litres and tins for rooms, walls, ceilings and exteriors.
Bricks per m², mortar and cost for any wall.
Concrete, breeze and aircrete blocks, with mortar and cost.
Why screed orders fall short
Picture this. The screeder arrives at eight, the mixer is turning by nine, and the cement runs out before lunch. The order looked correct on paper. It used the finished volume of the floor, and nobody allowed for shrinkage.
Dry sand and cement shrink by roughly a quarter once you add water. Consequently, a floor requiring 1 m³ of screed actually consumes approximately 1.33 m³ of dry materials. Ignore that, and every quantity on the delivery note falls short.
Order on dry volume: the calculator multiplies your floor volume by 1.33 before dividing it into sand and cement. Those figures match our sand calculator exactly.
How much sand and cement for 1 m³ of screed?
One cubic metre of 4:1 screed requires approximately 1.7 tonnes of sharp sand and 15.3 bags of cement. Round up to 16 bags.
How much does screed cost per m²?
Traditional screed typically costs £12 to £20 per m² installed. Liquid screed costs approximately £18 to £35, and smaller rooms cost proportionally more.
How to use the screed calculator
Select the tab that matches your floor, then complete the form from top to bottom. It works as a floor screed calculator, a liquid screed calculator and a cost estimator together.
- Sand and cement. Choose bonded, unbonded, floating or underfloor heating. The calculator recommends a sensible depth and warns you below the minimum.
- Liquid screed. Choose the construction and the pipe diameter. It checks the cover above the heating pipes and calculates the cubic metres to order.
- Levelling compound. Enter the average depth of the hollows. It then counts the bags of smoothing compound or renovation screed.
- Enter the floor area. Add rectangles for L-shaped rooms, or use a circle or a known total.
- Add prices if you have them. The calculator compares mixing your own, pre-mixed bags and ready-mixed screed, then highlights the most economical option.
Every result includes the typical installation price, so you can compare doing it yourself with hiring a professional screeder.
Which floor screed do you need?
Traditional screed combines sharp sand and cement, laid semi-dry and compacted by hand. Liquid screed is usually calcium sulphate, often called anhydrite, and a pump distributes it evenly.
| Screed | How it is laid | Best for |
|---|---|---|
| Bonded sand and cement | Stuck to a clean slab with a bonding coat | Thin levelling over sound concrete |
| Unbonded sand and cement | On a polythene membrane | Old slabs with damp or contamination |
| Floating sand and cement | On rigid insulation | New floors and extensions |
| Liquid calcium sulphate | Pumped in, then it flows level | Underfloor heating and larger areas |
| Levelling compound | Poured thin, from 1 mm | Smoothing before vinyl, wood or tiles |
Laying the concrete slab first? Our concrete calculator sizes the base underneath.
How thick should screed be?
Each construction method has its own minimum depth. Going thinner saves materials, but the floor eventually cracks, curls or separates from the slab.
| Construction | Sand and cement | Liquid screed |
|---|---|---|
| Bonded | 25 mm minimum, 40 mm ideal | 25 mm minimum |
| Unbonded | 50 mm minimum, 70 mm design | 30 mm minimum |
| Floating | 65 mm, or 75 mm for heavier loads | 35 mm minimum |
| Over underfloor heating | 65 mm total, 75 mm safer | 30 mm above the pipes |
Minimum screed thickness from BS 8204 guidance. Below 25 mm, use a levelling compound instead.
The Concrete Centre guide to floor screeds explains the reasoning. Excessively thick bonded screeds can debond, and unbonded screeds that are too thin can curl. With 16 mm heating pipes, liquid screed therefore requires 46 mm, so most installers specify 50 mm.
How much screed do I need per m²?
Each millimetre of depth requires one litre of screed per square metre. These figures use a 4:1 mix with 5% extra, identical to the calculator.
| Depth | Sharp sand per m² | Cement per m² | Laid weight per m² |
|---|---|---|---|
| 25 mm | 45 kg | 10 kg | 52 kg |
| 40 mm | 72 kg | 16 kg | 84 kg |
| 50 mm | 89 kg | 20 kg | 105 kg |
| 65 mm | 116 kg | 26 kg | 137 kg |
| 75 mm | 134 kg | 30 kg | 158 kg |
| 100 mm | 179 kg | 40 kg | 210 kg |
Sand at 1.6 t/m³ and cement at 1.44 t/m³. Laid screed weighs about 2.1 t/m³.
Screed is surprisingly heavy, so a 75 mm floor adds approximately 158 kg to every square metre. Consult a structural engineer before you screed over timber joists.
What is the best screed mix ratio?
Most UK floor screeds combine four parts sharp sand with one part cement. The Concrete Centre quotes a traditional range from 3:1 to 4.5:1.
| Mix | Use it for | Sand per m³ | Cement per m³ |
|---|---|---|---|
| 3:1 (strong) | Thin bonded screeds and heavy use | 1.6 t | 479 kg (19.2 bags) |
| 4:1 (standard) | Most homes and extensions | 1.7 t | 383 kg (15.3 bags) |
| 4.5:1 (lean) | Lightly loaded floating screeds | 1.74 t | 348 kg (13.9 bags) |
Per cubic metre of finished screed, before waste. Dry materials at 1.33 times the volume.
Use washed sharp sand, sometimes sold as concreting or grit sand. Our sand calculator explains why soft building sand produces a weak, dusty floor. Mix the screed semi-dry, so a squeezed handful holds its shape without wetting your palm.
How much does it cost to screed a floor?
Screeding contractors price by the square metre, and most include materials and pumping. The Trade2Base 2026 price guide gives these supply and lay rates for floors over 30 m².
| Screed | Typical depth | Laid price per m² (ex VAT) |
|---|---|---|
| Sand and cement, bonded | 25–40 mm | £12–£18 |
| Sand and cement, unbonded | 50 mm | £13–£19 |
| Sand and cement, floating | 65–75 mm | £14–£20 |
| Liquid screed | 40–50 mm | £18–£28 |
| Liquid screed over heating | about 50 mm | £20–£35 |
| Fibres added | Any | plus £1–£3 |
Floors under 20 m² usually pay a minimum charge of about £300 to £500. Pump hire costs about £300 to £600 a day.
Liquid screed price per m³ depends on the depth. At 50 mm, one cubic metre covers 20 m². Therefore £18 to £28 per m² equals £360 to £560 per m³ installed.
Our honest view? On floors over about 30 m², a professional screeder often costs little more than retail materials. Contractors buy materials at trade prices. A two-person gang can typically lay around 150 m² a day.
How long does screed take to dry?
The usual UK guideline is one day per millimetre for the first 40 mm. Thicker screed dries considerably more slowly, so allow two days for each additional millimetre.
| Depth | Sand and cement | Liquid screed |
|---|---|---|
| 25 mm | about 25 days | about 25 days |
| 40 mm | about 40 days | about 40 days |
| 50 mm | 50 to 60 days | about 60 days |
| 65 mm | 65 to 90 days | Rarely this thick |
| 75 mm | 75 to 110 days | Rarely this thick |
At about 20 °C with good ventilation. The lower figure follows the Concrete Centre rule of one day per millimetre up to 50 mm.
Light foot traffic is usually acceptable after a day or two. Before laying flooring, always test the moisture, because most coverings require 75% relative humidity or lower. With underfloor heating, liquid screed can typically begin force drying after about seven days.
How far does a bag of levelling compound go?
Self-levelling compound fills hollows from approximately 1 mm deep. Coverage depends on the powder weight per square metre for each millimetre. Two-part latex compounds suit timber floorboards and plywood.
| Average depth | Smoothing compound (1.6 kg) | Renovation screed (1.8 kg) |
|---|---|---|
| 2 mm | 7.8 m² per 25 kg bag | 6.9 m² per 25 kg bag |
| 3 mm | 5.2 m² | 4.6 m² |
| 5 mm | 3.1 m² | 2.8 m² |
| 10 mm | 1.6 m² | 1.4 m² |
| 20 mm | Too deep | 0.7 m² |
Coverage in kilograms per m² per millimetre of depth. Check your bag, then choose Custom in the calculator if it differs.
The Mapei data sheet says one bag of Ultraplan Renovation Screed 3240 covers about 6 m² at 3 mm. Its own mix density of 2,100 kg/m³ suggests nearer 4.7 m². We use the safer figure, so you will not run short during the pour.
Screed calculator examples for UK floors
We calculated each floor with the screed calculator, using its default settings.
Example 1: kitchen extension over underfloor heating
A 5 × 4 m floating screed at 75 mm, 4:1 with fibres
Example 2: the same floor in liquid screed
20 m² at 50 mm over 16 mm heating pipes
Liquid screed costs more here, yet it sits 25 mm thinner and dries several weeks sooner.
Example 3: bathroom levelling screed
6 m² bonded to the slab at 40 mm, 3:1
Example 4: hallway before new vinyl
12 m² of smoothing compound at an average 3 mm
Example 5: old tiles before new flooring
10 m² of fibre renovation screed at 15 mm
Sand and cement or liquid screed?
Both produce an excellent floor when installed properly. The right choice depends on heating, area, budget and timing.
| Factor | Sand and cement | Liquid screed |
|---|---|---|
| Floating depth | 65 mm minimum | 35 mm minimum |
| Over heating pipes | 65–75 mm in total | 30 mm above the pipes |
| Typical laid price | £12–£20 per m² | £18–£35 per m² |
| Speed | Laid and compacted by hand | Up to 2,000 m² a day by pump |
| Wet rooms and steel mesh | Suitable | Avoid both |
Our honest opinion? Over underfloor heating, we would choose liquid screed. It surrounds the pipes completely, sits thinner and warms the room sooner. For a small bathroom or a garage, traditional screed is more economical.
Screed mistakes that crack floors
These errors explain most cracked, dusty or hollow-sounding floors.
- Ordering on finished volume. Dry materials shrink, so order 1.33 times the floor volume.
- Using building sand. Soft sand produces a weak screed that dusts and cracks.
- Going too thin. A floating screed under 65 mm can crack over insulation.
- Skipping the fibres. Floors above heating pipes expand and contract with every heating cycle.
- Tiling too soon. Damp screed can leave tiles sounding hollow, as our hollow tiles guide explains.
- Forgetting the edge strip. Liquid screed requires a compressible strip around every wall.
Tiling the floor next? Our tile calculator counts the tiles, and our tile adhesive calculator sizes the adhesive.
Screed calculator FAQs
How the screed calculator gets its numbers
To work out screed quantities, the calculator multiplies your area by the depth and the waste allowance. For traditional screed, it then multiplies by 1.33 for the dry materials. Finally, it divides them according to the mix ratio.
Sharp sand weighs 1.6 t/m³ and cement 1.44 t/m³, the same as our sand and paving calculators. Installation prices come from 2026 UK contractor rates, and minimum depths follow BS 8204 guidance.
Remember the cement that ran out before lunch? Ordering on dry volume, with 5% extra, keeps the mixer turning until you complete the final bay. Prices checked in October 2026. Treat results as estimates, and confirm the specification with your screeder.
What floor are you screeding, and did you choose sand and cement or liquid screed? Tell us through our contact page. Real projects help us improve the calculator.