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Mixing concrete

Cement, sand, gravel and water quantities for a given volume and concrete class.

1 What concrete are you mixing?

2 How much concrete do you need?
m³

Select the concrete class and quantity – the mix is calculated instantly.

Concrete mixing ratio by class

Concrete is mixed from cement, aggregate (sand + gravel), and water. The ratio determines the resulting strength. It's given as cement : sand : gravel (by volume):

  • 1 : 4 : 4 base concrete, levelling layers (lower strength, ~C12/15)
  • 1 : 3 : 3 foundations, slabs, general use (~C16/20)
  • 1 : 2.5 : 3 loaded structures, columns (~C20/25)

How much water

Water is added at roughly half the weight of the cement (water/cement ratio ~0.5). Too much water weakens the concrete – the mix should be workable, not runny. Add it gradually.

Simplified "by shovel" mixing

For small quantities it's handy to count shovels: for a 1 : 3 : 3 ratio, for every shovel of cement add 3 shovels of sand and 3 shovels of gravel. It's not exact to the gram (shovels vary), but it's enough for undemanding concreting jobs (a curb, a fence post base).

How to mix it correctly

  1. Put some of the water in the mixer.
  2. Add the cement, mix to a paste.
  3. Add the sand and gravel.
  4. Top up with water to a workable consistency.
  5. Mix for 2–3 minutes until uniform, and use within an hour.

Note: ratios and consumption are approximate. The exact recipe depends on the aggregate size, sand moisture, and required strength. For load-bearing structures, follow the project specification.