Concrete Mix Calculator

What do concrete grades mean?

The grade tells you the compressive strength of the concrete after 28 days of curing. C20 means 20 newtons per square millimetre. Higher numbers mean stronger concrete.

Which grade should I use?

C20 (1:2:4)

General domestic work -paths, shed bases, non-structural slabs.

C25 (1:1.5:3)

Foundations, floor slabs, and light structural work.

C30 (1:1:2)

Reinforced structural work, driveways, heavy-duty floors.

C35 (1:0.75:1.5)

Heavy structural use -commercial foundations and industrial floors.

How does the calculator work?

The wet volume you enter is multiplied by a bulking factor of 1.54 to get the dry volume. That dry volume is split according to your chosen ratio. Cement density is 1,440 kg/m³, sand is 1,600 kg/m³, and aggregate is 1,500 kg/m³. Water is calculated at a 0.5 water-to-cement ratio by weight.