Screed calculator: sand, cement and liquid screed
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check your supplier's or maker's figures before ordering.
Short answer
A 5 × 4 m room screeded 65 mm deep needs 1.365 m³ of screed with 5% waste. At our typical 1:4 sand and cement mix, that's 511 kg of cement (21 bags at 25 kg) and 2.27 t of sharp sand. The calculator also handles screed laid to falls, pre-bagged screed and liquid screed.
The minimum thickness depends on how the screed is laid: see BS 8204 explained. Once you know the thickness, the screed drying time calculator gives a rule-of-thumb drying time.
Work out the volume of a floor screed, then the sand and cement, pre-bagged screed or liquid screed to order. Enter your measurements below; every figure we start from is shown and you can change it.
Worked example
| You enter | Value |
|---|---|
| Type of screed | Sand and cement |
| Floor area | Room: rectangle 5 m × 4 m |
| Laid to falls | No |
| Depth | 65 mm |
| Construction | Bonded to the slab |
| Waste allowance | 5% |
| Mix: parts sharp sand to 1 part cement | 4 parts |
| Dry-volume factor | 1.3 × |
| Cement density | 1,440 kg/m³ |
| Sharp sand density | 1.6 t/m³ |
| Cement bag size | 25 kg |
| Bulk bag size | 0.85 t |
Order: 21 × cement bags and 2.27 t of sharp sand
- Limit not yet confirmed Depth against the minimum thickness: 65 mm The BS 8204-1 minimum for this construction hasn't been confirmed yet: check the standard or the screed maker. UK-wide: BS 8204-1 (bonded screed). Check with the source.
| Result | Value |
|---|---|
| Screed (wet volume, with waste) | 1.365 m³ |
| Cement bags | 21 |
| Cement | 511.1 kg |
| Sharp sand | 2.27 t |
| Sharp sand bulk bags | 3 |
| Average depth | 65 mm |
| Area | 20 m² |
Show the working
- Wet volume: 20 m² × 65 mm × 1.05 (5% waste) = 1.365 m³
- Dry materials: 1.365 × 1.3 = 1.775 m³
- Cement: 1.775 ÷ (1 + 4) × 1,440 kg/m³ = 511.1 kg
- Sharp sand: 1.775 × 4 ÷ (1 + 4) = 1.42 m³ × 1.6 t/m³ = 2.27 t
- Cement bags: 511.1 kg ÷ 25 kg, rounded up = 21
How it works
- Average depth = (thinnest + thickest) ÷ 2 for a screed laid to falls
- Wet volume (m³) = area × average depth × (1 + waste)
- Sand and cement 1 : r: dry = wet × dry-volume factor; cement (kg) = dry ÷ (1 + r) × cement density; sand (t) = dry × r ÷ (1 + r) × sand density
- Pre-bagged: bags = wet volume (L) ÷ yield per bag, rounded up
- Liquid: order the wet volume; check the supplier's minimum load
Minimum thicknesses depend on the construction (BS 8204-1); over underfloor heating, follow the heating maker's cover.
Liquid screed is sold by the m³ with a minimum load: ask the supplier.
Our default (adjustable)
These are typical planning figures and our own allowances, not facts about your product. Change any of them in the calculator to match your bag, pack or tin.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Minimum thickness for this construction: Bonded to the slab | To be confirmed from the source | Regulation or HSE figure BS 8204-1 (minimum thickness, bonded screed) Not yet checked against the source | Source to be added by the Researcher brief v2 G3: minimum thicknesses by construction type from BS 8204-1, shown as Advisory. Researcher to source. |
| Minimum thickness for this construction: Unbonded (on a membrane) | To be confirmed from the source | Regulation or HSE figure BS 8204-1 (minimum thickness, unbonded screed) Not yet checked against the source | Source to be added by the Researcher brief v2 G3. Researcher to source from BS 8204-1. |
| Minimum thickness for this construction: Floating (on insulation) | To be confirmed from the source | Regulation or HSE figure BS 8204-1 (minimum thickness, floating screed) Not yet checked against the source | Source to be added by the Researcher brief v2 G3. Researcher to source from BS 8204-1. |
| Waste allowance | 5 % | Our assumption Not yet checked against the source | Our choice: change it to suit your job brief v2 G3 (test SC1 uses 5%). Researcher to confirm. |
| Mix: parts sharp sand to 1 part cement | 4 parts sharp sand to 1 cement | Our assumption Not yet checked against the source | Our choice: change it to suit your job brief v2 G3 (test SC1 uses a 1:4 sand–cement screed). Researcher to source to a cement or screed maker; check the maker's or specifier's mix. |
| Dry-volume factor | 1.3 × | Our assumption Not yet checked against the source | Our choice: change it to suit your job brief v2 G3 names factor.dry-screed as an assumption; test SC1 uses 1.3. Researcher to source to a screed or cement maker's mixing guidance. |
| Cement density | 1440 kg/m3 | Our assumption Not yet checked against the source | Our choice: change it to suit your job Typical planning figure with no source yet. Researcher to source it and reclassify as typical. |
| Sharp sand density | 1.6 t/m3 Sources range 1.6–1.7 t/m3 | Typical value Not yet checked against the source | aggregatecalculator.co.uk aggregate density table (checked 19 October 2026) Damp sand bulks; order by weight. |
| Cement bag size | 25 kg | Common UK size Not yet checked against the source | From your product Common UK cement bag. |
| Bulk bag size | 0.85 t | Common UK size Not yet checked against the source | builder.tools bulk bag figure (checked 19 October 2026) Varies by merchant; check yours. |
Regulations and standards
- BS 8204-1 (screeds): minimum thickness by construction type
Explained: BS 8204 (screeds).
BS 8204 is a British Standard used across the UK.
FAQs
How much screed do I need?
Multiply the floor area by the depth for the volume, and add a little for waste. A 5 × 4 m room at 65 mm is 1.3 m³, or 1.365 m³ with the calculator's 5% allowance. If the depth varies, enter the thinnest and thickest points and it uses the average.
How many bags of cement for screed?
Dry sand and cement take up more room than the wet mix, so the calculator scales the wet volume up by a dry-volume factor (1.3 by default) and then splits it by the mix ratio. For the 5 × 4 m room at 65 mm and a 1:4 mix, that's 511 kg of cement, or 21 bags at 25 kg, and 2.27 t of sharp sand: three 0.85 t bulk bags.
What is the screed mix ratio?
The calculator starts from 1 part cement to 4 parts sharp sand as a typical planning figure, not a recommendation. Use the mix in your screed or cement maker's guidance, or your builder's spec, and change the ratio in the calculator to match.
How thick should floor screed be?
It depends on whether the screed is bonded to the slab, laid on a membrane, floating on insulation or covering underfloor heating pipes. BS 8204-1 sets minimum thicknesses for each, and over underfloor heating the heating maker's figure for cover applies. See BS 8204 explained and enter your thickness in the calculator.
How do I work out a screed laid to falls?
Turn on "Laid to falls" and enter the thinnest and thickest points. The calculator averages them: 40 mm rising to 80 mm averages 60 mm, so the same 5 × 4 m room needs 1.26 m³ with waste.
How much liquid screed do I need?
Choose liquid screed and enter the area and depth. Liquid screed is ordered by the cubic metre, so the calculator gives the volume to order: 1.05 m³ for 20 m² at 50 mm with 5% waste. Ask the supplier about their minimum load and pumping access.
How long does screed take to dry?
It depends on the type of screed, how thick it is and the conditions. The screed drying time calculator gives a rule-of-thumb time from the thickness, but test the moisture before you lay a floor finish.