How many bags of concrete per m3? (+concrete calculator)

When you’re planning a project, you’ll need to figure out how many bags of concrete are needed for the job.

What does it take to lay one cubic meter of concrete?

This a question many people are asking so we thought we’d lay out a clear answer.

In this article, we’re going to learn how many bags of concrete per m3.

How much does a bag of concrete weigh?

Most concrete bags are 20 kg or 10 kg.

Concrete mix is a mixture of cement, water, and aggregates. These products simply need water added in line with the instructions, and to be mixed slowly until you have a workable consistency.

How many bags of concrete per m3?

You will require approximately 100 – 110 x 20kg Concrete Mix bags per m3.

The guidance varies slightly depending on the brand. For example, looking at the popular concrete mix available at Bunnings, we see the following:

  • Bastion 20kg Concrete Mix: 100 x 20kg Bags per cubic metre
  • Australian Builders 20kg Concrete Mix: 100 x 20kg Bags per cubic metre
  • Dingo Fast Set High Strength Concrete: 110 x 20kg Bags per cubic metre

Naturally, it will also vary based on how much water you use. The guidance is usually 2.3 – 2.4 litres per 20kg bag.

For the rest of the article, we err on the side of caution and assume 110 x 20kg bags per cubic metre for our calculations.

So, for example, if you require a 2m x 2m slab with a depth of 50mm, your calculation would be as follows:

2 x 2 x 0.05 = 0.2m3

0.2 x 110 = 22 bags of 20kg Concrete mix.

Concrete volume calculator

Use our concrete calculator below to calculate how many bags of concrete you need for your project.

Note that while it is pre-set with the assumption of 110 20kg bags per cubic metre, you can override this based on guidance from the concrete manufacturer you purchase from.

How many m3 are in a bag of concrete?

Now that we know how many bags are in one cubic metre, we can do the reverse calculation: knowing how many metres cubed are in a bag.

Let’s continue with the example using a 20kg bag of concrete.

If 110 x 20kg bags = 1m3

Then:

1 x 20kg bag = 0.01m3

So, if for example, you had a project requiring 1m x 0.2m with a depth of 50mm, you should be able to get away with one bag of concrete (as 1 x 0.2 x 0.05 = 0.01).

How many bags of concrete do you need for a 10×10 slab?

The calculation for the metres squared is to multiply the width (10 metres) by the length (10 metres).

This equals 100 square metres.

Now multiply by 0.1 (assuming a 10cm thick concrete slab) for the thickness in metres, which gives 10 cubic metres.

As discussed above, one cubic metre requires approximately 110 x 20kg Concrete Mix bags.

Therefore in order to fill 10 cubic metres, you will need 1,100 bags of concrete (10 x 110).

How many bags of concrete do you need for a 4×4 slab?

For a 4×4 slab, we can repeat the calculation above with the new measurements:

4 x 4 x 0.1 (assuming a depth of 10cm) = 1.6m3

One cubic metre requires approximately 110 x 20kg Concrete Mix bags.

Therefore, you will need 176 bags of concrete (1.6 x 110).