How to calculate concrete in cubic metres
Multiply the area in square metres by the thickness in metres. If your thickness is in millimetres, divide it by 1,000 first. One cubic metre (m³) is 1,000 litres or approximately 1.308 cubic yards.
Open the metric concrete calculator
How much concrete for a 3 m × 2 m slab?
At 100 mm thick, a 3 m × 2 m slab needs 0.60 m³ before allowance. The calculation is 3 × 2 × (100 ÷ 1,000). With a 10% allowance, the order estimate is 0.66 m³, or 660 litres. The allowance is adjustable. Use the finished dimensions and thickness specified for your project.
| Thickness | Base volume | With 10% extra |
|---|---|---|
| 75 mm | 0.450 m³ | 0.495 m³ |
| 100 mm | 0.600 m³ | 0.660 m³ |
| 150 mm | 0.900 m³ | 0.990 m³ |
How many 20 kg or 30 kg bags make a cubic metre?
Divide 1,000 litres by the yield on the bag and round up. The yield is the mixed volume. A bag’s dry weight alone cannot tell you how much concrete it makes.
| Product | Approximate yield | Bags for 1 m³ | Bags for 0.66 m³ |
|---|---|---|---|
| Australian Builders Concrete, 20 kg | 10 L | 100 | 66 |
| SAKRETE Canada Concrete Mix, 30 kg | 14 L | 72 | 48 |
What if my supplier quotes by the cubic yard?
Use the alternate volume shown under the main result, or switch the calculator to imperial. When comparing rates, make sure both quotes use the same unit and currency. See the ready-mix quote guide for a worked example with delivery and minimum orders.