Screed calculator
Estimate screed volume and material quantities from floor area, thickness, density, cement dosage, bag size and waste allowance.
Screed quantity estimate
Enter floor area, screed thickness and mix assumptions to estimate volume and materials.
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How does this tool work?
A traditional sand and cement screed is mixed from cement, sand and water, but it is ordered in bags and tonnes. This calculator starts from the area and average thickness to give the screed volume, the volume to plan with an allowance, the total dry material mass, the cement for the chosen mix rate, the number of bags and the sand still to order.
Raw volume is area × thickness in metres; the allowance increases it to cover hollows in the base and mixing losses. The total dry mass is that volume multiplied by the density of dry materials needed for one cubic metre of screed.
Cement is the planned volume multiplied by the mix rate in kg/m³, then converted into whole bags. Sand is the total dry mass minus the cement: mixing water is not counted.
Example: 25 m² of floor at 5 cm thickness represents 1.25 m³ of screed before waste. If the substrate is uneven, measure several points because a few millimetres across a large area can materially change the volume.
How to use this tool
Measure area and thickness
Enter the area to cover and the average thickness, measured at several points if the base is uneven.
Set the allowance
Raise it for an irregular base or a first screeding job.
Enter density and mix rate
Keep the suggested values as a starting point or use those from the specification or cement manufacturer.
Enter the bag weight
Common cement bags weigh 25 kg; the result is rounded up to whole bags.
Screed volume and mix rate
The mix rate is expressed in kilograms of cement per cubic metre of screed.
Volume to plan
V = A × t × (1 + allowance)
A in m², t in metres.
Cement
Mc = V × rate; bags = ⌈Mc ÷ B⌉
r in kg/m³, B bag weight.
Sand
Ms = V × ρ − Mc
ρ is the density of the dry materials.
- t
- average thickness (m)
- r
- cement rate (kg/m³)
- ρ
- dry materials per m³ of screed (kg/m³)
- a
- allowance as a fraction
The calculation applies to site-mixed sand and cement screed. Pumped liquid screed or bagged ready-mix screed is calculated from the volume or per-m² consumption stated by the manufacturer.
Use cases
Levelling screed before tiling
Order cement and sand for a room before laying tiles or glued wood flooring.
Screed over insulation
See how a greater thickness, often needed over insulation boards, changes the bag count.
Compare mix rates
See the cement difference between 250, 300 and 350 kg/m³ for the same area.
Examples
30 m² room at 5 cm
495 ÷ 35 = 14.1, rounded up to 15 bags. Sand is the difference between 3,300 kg and 495 kg.
Input
30 m², 5 cm, 10% allowance, 2,000 kg/m³, 300 kg/m³ cement, 35 kg bagsResult
1.5 m³ raw, 1.65 m³ to plan, 3,300 kg dry materials, 495 kg cement, 15 bags, 2,805 kg sand12 m² bathroom at 4 cm
A richer mix raises the cement; with 25 kg bags, 7.4 bags become 8.
Input
12 m², 4 cm, 10% allowance, 2,000 kg/m³, 350 kg/m³ cement, 25 kg bagsResult
0.48 m³ raw, 0.528 m³ to plan, 1,056 kg dry materials, 184.8 kg cement, 8 bags, 871.2 kg sandTips and best practices
- Set level screed rails or dots every 1 to 2 m before laying: the real average thickness depends on their accuracy.
- Convert sand to volume with the merchant’s bulk density if it is sold by the cubic metre or bulk bag rather than by the tonne.
- Protect fresh screed from draughts and sun to limit cracking caused by drying too fast.
- Respect the stated drying time before laying the finish, especially wood or vinyl that are sensitive to moisture.
Sources and references
Frequently asked questions
How many bags of cement for a 5 cm screed?
Each m² at 5 cm is 0.05 m³. At 300 kg/m³ with a 10% allowance you need about 16.5 kg of cement per m², so a 25 kg bag covers about 1.5 m².
Which mix should I use?
Traditional screeds are often around 1:3 to 1:5 cement to sand by volume, roughly 300 to 350 kg of cement per m³ for a typical floor screed. Follow the specification and the cement maker’s mix table.
What is the minimum screed thickness?
It depends on the type: bonded, unbonded and floating screeds over insulation have different minimums, set by standards such as BS 8204 in the UK or NF DTU 26.2 in France. Check them before entering yours.
Why is water not shown?
The calculator estimates materials to buy. Mixing water depends on the sand moisture and the consistency you want; it is adjusted on site.
How long does screed take to dry?
It depends on thickness, mix, temperature and ventilation. A common rule of thumb for cement screed is about a day per millimetre for the first 40 mm, to be confirmed by a moisture test before a sensitive floor finish.
Screed or slab: which calculator?
A screed is a thin finishing layer without structural reinforcement. For a load-bearing concrete slab, use the concrete calculator and, if needed, the rebar calculator.
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