How many bags of cement do I need to make 1 cubic metre of concrete?

Written by James McDonald

December 30, 2011

Currently doing fence posts and some small concrete pads around the house so I need to self mix the concrete

I keep searching for this type of thing on the internet:

Here is a good example of what is required from Boral’s Site

From my learnings:
1 Cement 2 Sand 3 Aggregate (gravel) is too strong. 16bags (costly)
1 Cement 2.5 Sand 4 Aggregate is OK for fence posts. 13bags of cement per cubic metre.

The more cement the more costly of course so don’t over do it.

Note: These are 20kg bags of General Purpose cement.


  1. Jonathan

    Can you assist by confirming how many 40kg bags of cement do I need per cubic metre volume?


    • James

      If it’s 13 bags of cement for 20kg bags it will be 6.5 bags of cement for 40kg bags.

      • Phillip

        Are you sure that’s 20 kg of cement per bag james?

        • James McDonald

          I’m not sure if I understand exactly what you mean, but in Australia the standard weigh for a bag of cement is 20kg.

    • Bob

      How many 20kg general purpose ready mixed concrete bags do i need for .56 cubic metres

  2. James

    If it’s 13 bags of cement for 20kg bags it will be 7.5 bags of cement for 40kg bags.

  3. Jarod

    I found from Boral 1m3 of cement you need 108 20kg bags (54-40kg) premix bags or For a one 20 kg bag equals 0.01m3.

    This should be easier to understand.

    • Damien

      Great thanks Jarod

  4. Allan O'Rourke

    How many bags of concrete do I need for a 3.1m x 3.1m x 110mm slab?

    • Drew

      C’mon Allan – thats just lazy ?
      3.1 x 3.1 = 9.61m2 x 0.11 = 1.05m3

      James’ estimates for 1cubic meter will be close enough for your slab.


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