How this calculator works
Screed volume is the area multiplied by the depth in metres, plus your waste allowance. A sand and cement screed mixed dry has to be about 1.3 times the finished volume, because the loose materials compact when they are wetted and rammed. The volume splits between cement and sand in the ratio you choose.
Worked example: a 4 × 3 m floor (12 m²) screeded 65 mm thick with 10% waste: 12 × 0.065 × 1.1 = 0.86 m³ (1.7 tonnes). Mixed 4.5 : 1, that takes about 292 kg of cement (12 bags of 25 kg) and 1.46 tonnes of sharp sand. As bagged dry screed mix it is about 69 bags of 25 kg.
Screed for common room sizes (65 mm, 4.5 : 1 mix, 10% waste)
Cement bags are 25 kg. Ready-mix bags assume 2 tonnes per m³.
| Room | Screed | Cement bags | Sharp sand | Ready-mix bags |
|---|---|---|---|---|
| 3 × 2.5 m | 0.54 m³ | 8 | 0.91 tonnes | 43 |
| 4 × 3 m | 0.86 m³ | 12 | 1.46 tonnes | 69 |
| 4 × 4 m | 1.14 m³ | 16 | 1.95 tonnes | 92 |
| 5 × 4 m | 1.43 m³ | 20 | 2.43 tonnes | 115 |
| 6 × 4 m | 1.72 m³ | 24 | 2.92 tonnes | 138 |
| 8 × 5 m | 2.86 m³ | 39 | 4.87 tonnes | 229 |
Tips before you buy
- Use sharp sand (also called concreting or screeding sand) and keep the mix as dry as you can: it should hold together when squeezed, like damp sand, and not slump.
- Lay it to levels set with screed rails or battens. Compact it as you go, and finish with a float.
- A floor over underfloor heating or insulation needs a floating screed, usually at least 65 mm. Check the heating maker's depth.
- Cover the screed and let it cure slowly, and keep off it for a day or two. Check it is dry before laying tiles or wood: a moisture meter is cheap.
- Mixing by hand is hard work: above about 5 m² a mixer, or ordering a mixer lorry or a pump-applied liquid screed, is worth thinking about.
Tools & materials for this project
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Frequently asked questions
How much screed do I need for a 4m x 3m room?
At 65 mm thick and with 10% extra, about 0.86 m³, which is about 1.7 tonnes. That is 12 bags of cement and about 1.5 tonnes of sharp sand at 4.5 : 1.
What is the ratio for a sand and cement screed?
A mix of 4 to 4.5 parts of sharp sand to 1 part of cement, by volume, is the usual choice for a screed. Richer mixes (3 : 1) are used for thin, bonded screeds.
How thick should a floor screed be?
At least 25 to 40 mm if bonded to the concrete below, 50 mm if unbonded, and 65 mm or more if floating over insulation or covering underfloor heating pipes.
How long does a screed take to dry?
A traditional sand and cement screed needs about a day for each millimetre of depth up to 50 mm, and longer beyond that. Test it with a moisture meter before laying tiles or wood.
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.