About this calculator
How many 50 kg bags of cement and how much concrete sand and 19 mm stone you need to mix a given amount of concrete on site, at low, medium or high strength.
How it’s calculated
The Concrete Society of Southern Africa gives the materials for 1 m³ of concrete. Low strength (house foundations): 290 kg cement, 0.65 m³ sand and 0.65 m³ stone. Medium strength (house floors, footpaths, driveways): 385 kg, 0.62 m³ and 0.62 m³. High strength (precast items, heavy-duty floors): 460 kg, 0.60 m³ and 0.60 m³. Multiply by the volume, add waste, and divide the cement by 50 kg. Sand and stone are rounded up to half cubes for ordering.
On site, the same mixes are batched as 2 bags of cement to 3½, 2½ or 2 wheelbarrows each of sand and stone, using a 65 litre builder’s wheelbarrow filled level.
Worked example
With these inputs:
- Concrete needed
- 1 m³
- Concrete mix
- Medium strength (house floors, footpaths, driveways)
- Waste allowance
- 10%
the result is:
- Cement
- 9 × 50 kg bags
- Concrete (incl. waste)
- 1.1 m³
- Per m³
- 385 kg cement, 0.62 m³ sand, 0.62 m³ stone
- Cement (50 kg bags)
- 9 bags
- Concrete sand
- 0.68 m³
Tips from the trade
- Use concrete sand and 19 mm or 26 mm stone, not plaster or building sand.
- Add only enough water to make the mix workable. Extra water weakens concrete.
- Keep new concrete damp for at least a week while it cures.
Common questions
How many bags of cement for 1 m³ of concrete?
About 6 bags for a low-strength foundation mix (290 kg), 8 bags for a medium-strength floor or driveway mix (385 kg) and 10 bags for a high-strength mix (460 kg), using the Concrete Society’s figures and rounding up to whole bags.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and SANS 10400 (the National Building Regulations) and your local municipality before ordering.