Cement calculator
When you mix a screed, a render or a masonry mortar yourself, the cement content depends on the mix: a stronger mix has more cement per cubic metre. The calculator takes the volume of the layer and the chosen mix and returns cement in kilograms and bags, plus the sand.
For small areas a pre-mixed dry product is often simpler and more consistent — its consumption is printed on the bag.
Your measurements
Result
- Mix volume
- 1.00 m³
- Cement needed
- 400 kg
- Cement bags
- 16 pcs
- Sand needed
- 1.10 m³
For concrete (with gravel) use the concrete calculator — the mix proportions are different.
How the calculation works
- Mix volume (m³) = length × width × layer thickness.
- Cement (kg) = volume × cement content: 400 kg/m³ for screed, 350 kg/m³ for render and 450 kg/m³ for masonry mortar.
- Bags = cement ÷ bag size, rounded up.
- Sand (m³) = volume × 1.10 (screed), 1.15 (render) or 1.05 (mortar).
Worked example
A 5 × 4 m screed, 5 cm thick, is 1 m³. At 400 kg of cement per m³ you need 400 kg — 16 bags of 25 kg — and 1.10 m³ of sand.
What the calculator assumes
- Sand is measured loose, which is why 1 m³ of mix needs more than 1 m³ of sand: part of the volume is lost when it is wetted and compacted.
- The cement contents are for an ordinary general-purpose cement (CEM II 42.5 class).
- The bag size is a field because bags differ between countries and brands (25 kg is common in much of Europe).
When to adjust the result
- For concrete (with gravel) use the concrete calculator — the proportions are different.
- Pre-mixed screeds, renders and mortars have their own consumption on the bag; use that instead.
- Structural work follows the mix specified in the project, not a rule of thumb.
Frequently asked questions
How much cement for 1 m³ of screed?
With a 1:3 mix, about 400 kg of cement and 1.1 m³ of loose sand per cubic metre of screed — 16 bags of 25 kg.
Can I use the same mix for render and screed?
Not ideally: renders are usually leaner (more sand) so they don't crack, screeds a little richer. Follow the mix recommended for the job or use a pre-mixed product.