# 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).