Concrete Mix Ratios — Quick Reference
Concrete Mix Ratios — Quick Reference
Common Mixes
| Use | Designation | Ratio (C:S:A) | Strength |
|---|---|---|---|
| General purpose (paths, bedding) | GEN1 | 1 : 3 : 6 | 10–15 N/mm² |
| Foundations (strip footings, trench fill) | GEN3 | 1 : 2 : 4 | 20–25 N/mm² |
| Driveways, garage floors | C25 / PAV1 | 1 : 2 : 4 or 1 : 1.5 : 3 | 25 N/mm² |
| Posts, kerb haunching | GEN0 / GEN1 | 1 : 3 : 6 | 10–15 N/mm² |
| Structural slabs (reinforced) | RC30 / C25/30 | 1 : 1.5 : 3 | 30 N/mm² |
Water Guide (Hand Mixing)
- • Roughly 0.5 litres per kg of cement
- • Too wet = weaker concrete
- • Too dry = won't compact properly
Coverage (per 25kg bag)
| 1 : 3 : 6 (GEN1) | ~0.10 m³ |
| 1 : 2 : 4 (GEN3) | ~0.07 m³ |
| 1 : 1.5 : 3 (C25) | ~0.05 m³ |
Key Points
- • BS 8500 uses designated mixes — ratios are rules of thumb for hand mixing
- • Ready-mix is specified by designation, not by ratios
- • All ratios assume CEM I cement and 20mm aggregate
- • Minimum 28 days curing for full design strength
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