Concrete Calculator
Work out how much concrete you need for a slab, footing, column or pile — plus the cement bags, sand and aggregate by mix ratio (M10, M15, M20, M25 or custom). Free, instant, no login.
How to calculate concrete
First work out the wet volume from the element's dimensions:
Volume (m³) = Length × Width × Thickness (all in metres)
Then convert to the dry volume of materials, because dry cement, sand and aggregate take up more space than the finished wet concrete:
Dry volume = Wet volume × 1.54
Finally split the dry volume by the mix ratio (cement : sand : aggregate). One 50 kg bag of cement is about 0.0347 m³, so the calculator converts the cement volume into bags automatically.
Material per cubic metre of concrete
| Mix | Ratio | Cement | Sand | Aggregate |
|---|
| M10 | 1:3:6 | ≈ 4.5 bags | ≈ 0.47 m³ | ≈ 0.94 m³ |
| M15 | 1:2:4 | ≈ 6.3 bags | ≈ 0.44 m³ | ≈ 0.88 m³ |
| M20 | 1:1.5:3 | ≈ 8.0 bags | ≈ 0.42 m³ | ≈ 0.84 m³ |
| M25 | 1:1:2 | ≈ 11.0 bags | ≈ 0.39 m³ | ≈ 0.77 m³ |
Based on 50 kg cement bags, a 1.54 dry-volume factor and typical densities. Always confirm against your project's approved mix design.
Frequently asked questions
How do you calculate concrete volume?
Multiply length × width × thickness in metres. A 5 × 4 m slab at 150 mm is 5 × 4 × 0.15 = 3 m³. For round columns use π/4 × diameter² × height.
How much cement is in 1 m³ of M20 concrete?
About 8 bags (≈ 400 kg), with roughly 0.42 m³ sand and 0.84 m³ aggregate, based on the 1:1.5:3 ratio and the 1.54 dry-volume factor.
Why multiply by 1.54?
Dry materials have voids and bulk up, so they occupy ~54% more volume than the final wet concrete. The factor converts wet volume to the dry quantity you must buy.
Is this calculator free?
Yes — free, no login. For a full BOQ from your drawings, SteelConnect's AI estimation gives a free first estimate.