May 21st 2019

Ever wondered how much reinforcing mesh you need to put into a concrete driveway, house slab or patio area? Take out the guesswork, and the “she’ll be right” approach to laying the perfect slabs every time by using a simple formula.

This industry standard formula is used all over Australia to calculate the amount of reo mesh you need before laying a concrete slab – And you have probably guessed it, we use it too! For 28 years to be exact.

So, let’s get started.

A person pouring wet concrete onto a concrete slab foundation

The Mesh calculator

Firstly, you need to calculate the area of your concrete slab. To do this simply multiply the length of the slab by the width.

Here is the formula: Length x Width = Slab Area (m2)

For example:

Grey rectangle representing a slab area that is 10 by 12 metres with measurements

For measuring a more complex slab design, try to break the total area into separate rectangles or squares. Calculate each one and then add them all together to find your total area, for example:

Two grey rectangles in an L-shape representing a slab area of 180 metres squared

Now that you have your area calculation, you need to divide the area by 12.5. This will give you the number of steel mesh sheets required to reinforce your concrete slab.

Here is the formula: Slab Area (m2) ÷ 12.5 = Total number of 6m x 2.4m sheets

For exmaple:

A visual representation of a slab area that is 261 metres squared

Calculating the reinforcing accessories

Bar chairs

Generally, a minimum of 22 bar chairs per sheet of 6m x 2.4m mesh is required. Otherwise, you can divide the slab area by 0.56. Quick tip; Bar chairs are commonly sold in bags of 100, therefore, ensure you round up to the nearest hundred.

Here is the formula:
Slab Area (m2) ÷ 0.56 = Total number of chairs
Example: 250m2 ÷ 0.56 = 466.4 (Round up to 500)

Polythene Film

Building polythene film or commonly referred to as poly, is sold in a roll that covers 200m2. Generally, it’s calculated that a single roll covers 180m2 instead of 200m2 as this allows for overlapping.

Here is the formula:
Slab Area (m2) ÷ 180 = Total number of poly rolls.

And that’s it, you are ready to purchase your reinforcing products and get your next slab underway. We love to see local builders doing their trade: send through any slab images too and we will feature you on our social pages, Have any questions or need any recommendations? Don’t hesitate to give us a call or flick us through an email.