Concrete Calculator
Work out exactly how much ready-mix you need in under a minute.
How to Use the Calculator
Pick a shape
Choose the shape that best matches the area you need to fill: rectangle, triangle, or circle.
Enter dimensions
Type in the length, width (or diameter) and depth. Use the preset depths or enter your own.
Adjust wastage
We add 5 % by default. Increase it for uneven ground or complex formwork.
Add more shapes
For multi-area projects, tap “Add Another Shape” and the totals combine automatically.
Tips for Accurate Measuring
- Measure depth at several points and use the average, as ground is rarely level.
- Round up rather than down. A small surplus is far better than running short mid-pour.
- Allow 5 to 10% wastage for spillage, uneven sub-bases, and formwork tolerances.
- Break irregular shapes into simpler ones and use “Add Another Shape” to combine them.
How to Calculate How Much Concrete You Need
To work out how much concrete you need, multiply the length by the width by the depth, all in metres, to get the volume in cubic metres (m3). For a circular area, use pi times the radius squared, times the depth. Ready-mix concrete is ordered by the cubic metre, so add 5 to 10 percent for wastage and round up to the nearest tenth.
For example, a slab 4m long, 3m wide and 100mm (0.1m) deep works out at 4 x 3 x 0.1 = 1.2m3. Adding 5 percent for wastage gives about 1.26m3, so you would order 1.3m3. The calculator above does this automatically and lets you combine several areas in one estimate.
As a rule of thumb, one cubic metre of concrete covers roughly 10 square metres at 100mm deep and weighs about 2.3 to 2.4 tonnes. For a full walkthrough with project examples, see our guide on how much concrete you need. If you are not sure which mix is right, our concrete mix grades guide explains the options, or you can browse our concrete mixes and order online.
Concrete Calculator FAQs
How do I calculate how much concrete I need?
Multiply length by width by depth in metres to get the volume in cubic metres. For a circle, use pi times the radius squared, times the depth. Add 5 to 10 percent for wastage. Our calculator does this for you and combines multiple areas.
How is ready mix concrete measured and sold?
Ready mix concrete is measured and sold by the cubic metre (m3). One cubic metre covers about 10 square metres at 100mm deep. Pricing is per cubic metre, so it helps to round your estimate up to the nearest tenth of a metre.
How much does a cubic metre of concrete weigh?
One cubic metre of concrete weighs roughly 2.3 to 2.4 tonnes, depending on the mix and aggregate. Weight matters for site access and ground bearing, but you order concrete by volume in cubic metres, not by weight.
How much extra concrete should I order?
Order 5 to 10 percent more than your measured volume to allow for spillage, uneven sub bases, and formwork tolerances. Running short mid pour is far more costly than a small surplus, so it is better to round up.
What depth of concrete do I need?
Common depths are 100mm for shed bases and paths, 100 to 150mm for domestic driveways, and 150mm or more for heavy use. Foundations are deeper and project specific. If in doubt, ask our team or read our concrete mix grades guide.