Concrete Calculator — Concrete Quantity Calculator
Calculate the amount of concrete needed for slabs, columns, beams, or footings. Get cement, sand, and aggregate quantities.
By SwiftCalcTools Editorial Team · Formula verified
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How to Use Concrete Calculator
- 1Enter the required values in the input fields above.
- 2Click the Calculate button or results update instantly as you type.
- 3View your results in the output panel below the inputs.
- 4Adjust any values to recalculate instantly.
Frequently Asked Questions
When concrete ingredients (cement, sand, aggregate) are mixed wet, the paste fills the voids between particles, reducing volume. Dry materials have ~54% more volume than the wet concrete they produce. So: dry volume = wet volume × 1.54. Always apply this factor when calculating material quantities.
"M" stands for Mix and the number is the characteristic compressive strength in N/mm² (MPa) at 28 days. M15 (1:2:4) is used for light construction like pathways. M20 (1:1.5:3) is the most common for slabs, columns, and beams. M25 (1:1:2) is used for high-strength applications. Higher grades use design mix ratios, not nominal.
For M20 mix (1:1.5:3): approximately 8 bags (50kg each) per m³ of wet concrete. For M15: ~7 bags. For M25: ~12 bags. The exact count depends on the dry volume factor and cement density (1440 kg/m³). Always add 5–10% extra for wastage.
The water-cement (W/C) ratio determines concrete strength and workability. Lower W/C = stronger concrete. Typical values: M15: 0.60, M20: 0.50, M25: 0.45. Too much water weakens concrete; too little makes it unworkable. For 50kg cement, W/C 0.50 means 25L water per bag.