Cement Ratio Calculator
Calculate cement bags required for a concrete mix from wet volume and mix ratio.
The finished, poured volume — use the Concrete Slab Calculator to find this first.
Formula
Cement Bags Required (50kg) = ((wetVolume * 1.54) / (cementRatio + sandRatio + aggregateRatio)) * cementRatio / 0.035
Dry construction materials (cement, sand, aggregate) occupy roughly 54% more volume before mixing than the final wet concrete volume, because water fills the voids between dry particles during mixing. To estimate cement quantity, the wet volume is first multiplied by 1.54 to get the required dry volume, which is then divided among the ratio parts. The cement's share is converted to bags by dividing by 0.035 m³ — the standard volume of one 50kg bag of cement.
Worked Example
- 1 Calculate dry volume: 2 m³ × 1.54 = 3.08 m³
- 2 Total ratio parts: 1 + 2 + 4 = 7
- 3 Cement volume: (3.08 ÷ 7) × 1 = 0.44 m³
- 4 Convert to bags: 0.44 ÷ 0.035 ≈ 12.6 bags
Result: Approximately 13 bags of cement (50kg each)
Video walkthrough for Cement Ratio Calculator — coming soon
Frequently Asked Questions
Why multiply by 1.54 for dry volume? +
Dry, loose materials have air gaps between particles that close up when water is added and the mix compacts, so more dry material is needed than the final wet volume suggests. 1.54 is the industry-standard factor for this shrinkage.
What mix ratio should I use for a house foundation? +
A 1:2:4 or 1:1.5:3 ratio is commonly used for foundations, but the correct ratio depends on the required compressive strength — check local building codes or consult a structural engineer for load-bearing work.