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Concrete calculator

Calculate how much cement, sand and aggregate you need to prepare concrete. Choose the concrete class and volume — the calculator gives the proportions of the ingredients.

Reviewed byRedakcja Liczbnik
Calculator
m³
Concrete mix compositionCement (kg)300
Sand (kg)
600
Gravel (kg)
1,100
Water (l)
190
Cement in 25 kg bags (pcs)
12

How we calculate the concrete mix

We calculate using standard proportions for the given concrete class (water-to-cement ratio, cement content per m³).

Example: 1 m³ of B20 concrete

B20 concrete: cement 350 kg, sand 650 kg, gravel 1200 kg, water about 175 l.

Frequently asked questions

What do concrete classes like B20 mean?

The class indicates the compressive strength. B20 (about C16/20) is common for footings and slabs, while higher classes suit heavier loads.

How much cement is in 1 m³ of B20 concrete?

Roughly 350 kg of cement per cubic metre, along with about 650 kg of sand, 1200 kg of gravel and 175 l of water.

What is the water-to-cement ratio?

It is the weight of water divided by the weight of cement. A lower ratio gives stronger, more durable concrete but is harder to work.

Can I mix concrete by hand?

Small amounts can be hand-mixed, but for slabs and foundations a mixer or ready-mix delivery gives more consistent quality.

Should I add a margin to the volume?

Yes, add about 5–10% to allow for spillage, uneven ground and slight compaction so you do not run short mid-pour.

When should I use ready-mix instead?

For large pours or structural, load-bearing elements, certified ready-mix concrete ensures consistent strength and saves time.

Indicative result

The result is for guidance only. Use concrete from a certified plant for load-bearing structures.

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