Calculator
Concrete Mix Calculator
Tell it the size of the slab, beam or footing and the grade. It gives you the number of cement bags, and the sand and aggregate in cubic feet.
The formula
What this assumes
- The 1.54 factor covers the shrinkage when dry material is mixed with water. This is standard practice.
- Water-cement ratio is taken as 0.50. Your site engineer may change it.
- No wastage is added. Add 3 to 5% for site wastage when ordering.
- M20 and above should ideally be design mix, not nominal mix. For small work nominal mix is fine.
- For big pours, ready-mix concrete usually works out cheaper and more reliable.
Common questions
Which grade should I use?
Follow your structural drawing. As a rough guide: M20 for slabs, beams and columns in a normal house. M25 where the engineer asks for it. M10 or M15 only for levelling course (PCC) below foundation.
How many cement bags in 1 cubic metre of M20?
About 8 bags. The calculator gives the exact figure for your volume.
What is the difference between M20 and M25?
The number is the strength in N/mm2 after 28 days. M25 is stronger and uses more cement. Do not upgrade on your own to feel safer. Use what the drawing says.
Why multiply by 1.54?
Dry cement, sand and aggregate have air gaps. When water is added and it is compacted, the volume reduces. So you need about 54% more dry material than the finished wet volume.