Concrete calculator
Free toolEnter your slab measurements (or the volume directly) and calculate how much cement, sand, gravel and water you need with the standard 1:2:4 mix.
Mix needed
How to use it
- Enter the length, width and thickness of the slab or trench.
- Read the concrete volume in cubic metres.
- Check the breakdown of cement, sand, gravel and water for mixing on site.
What it works out and how
Volume is length times width times thickness. The mix uses a 1:2:4 ratio (cement, sand and gravel), which per cubic metre of concrete takes about 300 kg of cement, that is 12 bags of 25 kg, 600 kg of sand (0.42 m³), 1,200 kg of gravel (0.83 m³) and 180 litres of water. It is a general-purpose mix, not a structural calculation.
Frequently asked questions
Should I order extra concrete?
Yes, 5 to 10% more. The ground is never perfectly level, and running short mid-pour forces a cold joint.
How thick should a slab be?
For foot traffic 8–10 cm is usually enough; for vehicles, 12–15 cm with mesh. Structural elements must be designed by an engineer.
Mixer or truck?
Up to half a cubic metre can be mixed on site. From one or two cubic metres, ready-mix pays off in effort and consistency.