Concrete Mix Calculator
Enter slab size and mix ratio to estimate cement, sand, aggregate, and water.
Assumptions used: cement density = 1440 kg/m³, sand density = 1600 kg/m³, aggregate density = 1500 kg/m³.
Why a concrete mixing ratio calculator is useful
When you are planning a slab, footing, driveway, post base, or small DIY concrete project, one of the biggest questions is: How much cement, sand, and aggregate do I need? A concrete ratio calculator helps you answer that quickly and consistently. Instead of guessing or over-ordering, you can estimate your total materials before you start.
This matters because incorrect proportions can affect strength, workability, and durability. Too much water weakens concrete. Too little cement can lead to poor bonding. Too much aggregate can make placement and finishing difficult. A simple calculator keeps your mix design organized and repeatable.
How this calculator works
1) Compute wet concrete volume
The tool first calculates volume from your dimensions: Volume = Length × Width × Thickness. Thickness is converted from centimeters to meters.
2) Convert wet volume to dry volume
Dry ingredients occupy more volume than finished concrete due to voids and compaction. That is why builders often use a dry volume factor (commonly around 1.52 to 1.57). This calculator uses 1.54 by default and also adds wastage.
3) Split dry volume by mix ratio
For a nominal ratio like 1:2:4, the total parts are 7. Cement gets 1/7, sand gets 2/7, and aggregate gets 4/7 of the adjusted dry volume.
4) Convert to practical units
- Cement volume is converted to kilograms and then to number of bags.
- Sand and aggregate are shown in cubic meters and estimated kilograms.
- Water requirement is estimated from the water-cement ratio.
Common nominal concrete ratios
- 1:5:10 (M5) – very lean mixes, usually non-structural.
- 1:3:6 (M10) – low-strength blinding and basic flooring layers.
- 1:2:4 (M15) – common for general household concrete work.
- 1:1.5:3 (M20) – common structural-grade nominal mix in many regions.
- 1:1:2 (M25) – richer mix for higher strength requirements.
Always follow your local code and project specifications. For structural members, use an engineer-approved design mix rather than only nominal proportioning.
Quick field tips for better concrete quality
- Measure materials consistently (same bucket size or calibrated containers).
- Use clean, well-graded sand and aggregate.
- Add water gradually—do not flood the mix.
- Mix thoroughly to avoid weak pockets.
- Place and compact promptly to reduce honeycombing.
- Cure concrete properly (at least 7 days; longer is better).
Example scenario
Suppose you are casting a slab that is 5 m × 3 m × 10 cm using a 1:2:4 mix. The calculator estimates your wet volume, adjusts for dry materials and wastage, then outputs cement bags, sand, aggregate, and water. This lets you compare supplier quotes and plan transport with confidence.
Important note
This concrete material calculator is intended for planning and estimation. Site moisture, compaction, aggregate grading, and workmanship can change actual consumption. For structural concrete (columns, beams, suspended slabs, foundations), consult a licensed structural engineer and use approved mix designs.