Concrete Calculator

How to Calculate Concrete Volume

Getting the right amount of concrete for your project is essential — order too little and you face delays, order too much and you waste money. Our concrete calculator converts your slab, footing, or post hole dimensions into the exact volume of concrete you need, expressed in cubic metres (m³). This is the standard unit used by Australian concrete suppliers when quoting and delivering.

Enter the length, width, and depth of your pour area in metres. For cylindrical shapes like post holes or round columns, enter the diameter and depth. The calculator returns the volume in cubic metres, along with an estimated number of pre-mixed bags for smaller DIY projects.

Common Concrete Applications

Concrete is used in a wide range of residential and commercial projects across Australia. Driveways typically require a slab thickness of 100–125mm, while garage floors and paths can be as thin as 75–100mm. Footings for retaining walls, house stumps, and fence posts are usually deeper — 300–600mm depending on the load and soil conditions.

For structural work such as house slabs and footings, always consult an engineer for the correct specifications. Building codes and soil classifications vary across Australia, and getting the depth, reinforcement, and concrete grade wrong can compromise the integrity of the structure.

Ordering Concrete in Australia

Ready-mix concrete from a batch plant is the most practical option for pours larger than about 0.5 m³. Most suppliers have a minimum order of 0.2–0.3 m³, and you should always order 5–10% more than your calculated volume to account for spillage, uneven ground, and formwork irregularities. Standard residential concrete in Australia is typically 20–25 MPa (megapascals) strength, with 32 MPa or higher used for driveways and structural elements.

For smaller jobs, pre-mixed bags from hardware stores like Bunnings are convenient. A standard 20 kg bag yields approximately 0.009 m³ of mixed concrete — so a 1 m³ pour would require around 110 bags. Our calculator shows both options so you can choose the most cost-effective approach for your project size.