Concrete calculator

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

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

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.

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

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

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