Concrete Calculator South Africa
Enter dimensions or a volume — get bags of cement, m³ of sand and stone. Based on PPC and AfriSam mix guides.
75–100 mm slab, 150 mm footing
10% recommended for slabs
Materials needed
for 2.20 m³ (1:2:3 mix)Cement (50 kg)
13 bags
OPC Portland
Sand
1.36 m³
sharp/plaster sand
Stone (19 mm)
2.05 m³
aggregate
Water
303 L
approx. (0.5 w/c)
How this is calculated
Mix ratios from PPC / AfriSam mix guide. Quantities are dry volumes before mixing — actual compacted concrete volume is lower. Always add 10% wastage for slabs. Water quantity is approximate (0.5 water:cement ratio); adjust for workability on site.
Common questions
How many bags of cement do I need for a 1:2:3 mix?
For 1 m³ of M20 (1:2:3) concrete you need approximately 5.5 × 50 kg bags of OPC cement, 0.62 m³ of sand, and 0.93 m³ of 19 mm stone. Always add 10% wastage for slabs. The calculator handles all of this automatically.
What is the difference between a 1:2:3 and 1:3:6 mix?
A 1:2:3 mix (M20) is a structural-grade concrete used for floor slabs, footings, beams, and columns. A 1:3:6 mix (M10) is a weaker, more economical mix used for blinding, levelling screeds, and non-structural fills. The 1:1.5:3 (M25) is a high-strength mix for industrial floors and heavily loaded slabs.
How deep should a concrete floor slab be?
A domestic floor slab in South Africa is typically 75–100 mm thick (75 mm is minimum per SANS 10400, 100 mm is common practice). Driveways are usually 100–150 mm. Structural ground-floor slabs can be 150–200 mm with reinforcing.
Why are my calculated quantities dry volumes?
Concrete ingredients are measured as dry volumes before mixing. When cement, sand, stone, and water are combined, the cement paste fills the voids between the aggregates, so the final compacted volume of concrete is less than the sum of the dry ingredients. This is why you need slightly more dry material than the final volume suggests.
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