How to Use the Concrete Calculator

Choose the type of concrete section you want to calculate and enter its dimensions. You can add multiple slabs, footings, columns or round holes.

The calculator estimates:

• Concrete volume in cubic metres;
• Concrete volume in litres;
• Extra volume for wastage;
• Number of premix concrete bags;
• Estimated premix bag cost; and
• Estimated ready-mix concrete cost.

How Do You Calculate Concrete Volume?

For rectangular concrete sections such as slabs and strip footings:

All dimensions must be converted to metres before calculating cubic metres.

Concrete Slab Example

How to Calculate Concrete for a Footing

A rectangular strip footing uses the same volume formula:

For example, a 10 metre footing that is 400 mm wide and 300 mm deep:

10 × 0.4 × 0.3 = 1.2 m³

How to Calculate Concrete for a Round Hole or Pier

For a cylindrical post hole or pier:

The radius is half the diameter.

How Many Litres Are in One Cubic Metre of Concrete?

One cubic metre equals:

Therefore, 0.5 m³ of concrete is approximately 500 litres.

How Much Extra Concrete Should I Order?

Ordering slightly more than the exact calculated volume can help account for:

• Uneven excavation;
• Spillage;
• Variation in slab thickness;
• Formwork differences;
• Ground irregularities; and
• Measurement error.

A wastage allowance of around 5% to 10% is commonly used for planning, although actual requirements depend on the project.

How Many Bags of Concrete Do I Need?

Premix concrete bags provide a stated approximate yield after mixing. Use the yield shown on your chosen product.

The calculator rounds the result up to the next whole bag.

Concrete Bag Example

If a bag yields approximately 0.009 m³ and you require 0.18 m³:

Premix Bags vs Ready-Mix Concrete

Premix bags can be suitable for smaller jobs such as:

• Fence posts;
• Small pads;
• Minor repairs;
• Letterbox footings; and
• Small garden structures.

Ready-mix concrete delivered by truck may be more practical for larger slabs and high-volume pours.

How Thick Should a Concrete Slab Be?

Slab thickness depends on the intended use, soil, reinforcement, design loads and engineering requirements.

Examples often seen in residential work may include around 100 mm for some light-duty slabs, but this calculator does not determine the correct structural thickness for a project.

Use the thickness specified by your plans, engineer or relevant construction requirements.

Can I Use This Calculator for Driveways?

Yes. Enter the driveway length, width and concrete thickness as a slab.

For irregular driveway shapes, divide the project into smaller rectangular sections and add each section separately.

Can I Use It for Concrete Paths?

Yes. Enter the path length, width and depth as a rectangular slab or footing.

Can I Calculate Multiple Concrete Areas?

Yes. Click Add Another Section and enter each section separately. The calculator automatically combines all volumes.

Concrete Calculator Assumptions

This calculator assumes:

• Dimensions are measured accurately;
• Rectangular sections have uniform depth;
• Round holes and columns are cylindrical;
• Millimetre dimensions are converted to metres;
• Bag yield is entered correctly from the product information;
• Bag quantities are rounded up;
• Ready-mix pricing is entered per cubic metre;
• Delivery, pump and minimum-load charges are not included;
• No reinforcement or formwork is calculated; and
• Results are planning estimates only.

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