Concrete Mix Calculator
Calculate exactly how much cement, sand, and gravel you need for your concrete mix.
📖 What is a Concrete Mix Calculator?
A concrete mix calculator helps you determine the exact quantities of cement, sand, and coarse aggregate (gravel or crushed stone) needed to prepare a specific volume of concrete for your construction project. Getting the mix proportions right is critical - too much cement wastes money, too little produces weak concrete.
Concrete is one of the most versatile and widely used construction materials in the world. It consists of cement (the binding agent), fine aggregate (sand), coarse aggregate (gravel or crushed stone), and water. The proportions of these ingredients determine the concrete's strength, workability, and durability.
In India and many countries, concrete grades are designated as M10, M15, M20, M25, etc., where M stands for Mix and the number represents the characteristic compressive strength in MPa (mega-pascals) after 28 days of curing.
📐 Formula
Dry Volume = Wet Volume × 1.54
(The 1.54 factor accounts for shrinkage/compaction when water is added)
For a mix ratio of 1:x:y (cement:sand:aggregate):
Total parts = 1 + x + y
Cement Volume = (1 / Total parts) × Dry Volume
Sand Volume = (x / Total parts) × Dry Volume
Aggregate Vol = (y / Total parts) × Dry Volume
Cement (kg) = Volume × 1440 kg/m³ (density of cement)
Bags = Cement (kg) / 50 kg per bag
📖 How to Use This Calculator
1
Enter the volume of concrete needed in cubic metres (length × width × thickness).
2
Select the mix ratio - M20 (1:1.5:3) is standard for most structural work.
3
Click Calculate - get cement bags, sand volume, and aggregate volume.
💡 Example Calculations
Example 1 - M20 concrete for a 5m × 4m × 0.15m slab
1
Volume = 5 × 4 × 0.15 = 3 m³
2
Dry volume = 3 × 1.54 = 4.62 m³
3
Total parts = 1 + 1.5 + 3 = 5.5
4
Cement = (1/5.5) × 4.62 = 0.84 m³ = 1,210 kg = 25 bags
5
Sand = (1.5/5.5) × 4.62 = 1.26 m³
6
Aggregate = (3/5.5) × 4.62 = 2.52 m³
Example 2 - M25 for 2m × 2m × 0.3m column base
1
Volume = 2 × 2 × 0.3 = 1.2 m³
2
Dry vol = 1.2 × 1.54 = 1.848 m³
3
Cement = (1/4) × 1.848 = 0.462 m³ = 665 kg = 14 bags
Frequently Asked Questions
What does M20, M25 concrete mean?
The M stands for Mix and the number is the characteristic compressive strength in MPa after 28 days. M20 concrete has a strength of 20 N/mm² and a mix ratio of 1:1.5:3 (cement:sand:aggregate). M25 (1:1:2) is stronger and used for heavier structural applications.
What is the dry volume multiplier?
When you mix dry cement, sand, and aggregate with water, the mixture compacts and the volume decreases. To get 1 m³ of wet concrete, you need approximately 1.54 m³ of dry ingredients. This 1.54 factor accounts for the compaction/voids in the mix.
How many bags of cement per cubic meter of M20 concrete?
For M20 (1:1.5:3), the cement quantity per m³ of concrete is approximately 8 bags (400 kg or 50 kg × 8). This is for a water:cement ratio of 0.45-0.5.
Can I use any aggregate for concrete?
No - aggregate should be clean, hard, and well-graded. Coarse aggregate (crushed stone, gravel) size is typically 10-20mm for structural concrete. Fine aggregate (sand) should be free of clay and organic material. Never use sea sand without washing as it contains salts that corrode steel reinforcement.
How much water do I add to concrete?
The water-cement ratio (w/c) critically affects strength. Typical ratios: M20 = 0.45-0.55, M25 = 0.40-0.45, M30 = 0.35-0.40. Less water = stronger concrete, but too little makes it unworkable. For practical site work, add water gradually and test workability with a slump test.
What concrete mix ratio should I use for a house slab?
For a residential floor slab (non-structural), M20 concrete (1:1.5:3 cement:sand:aggregate) is standard in India and provides 20 MPa compressive strength. For RCC structural slabs (roof, beams), M25 (1:1:2) or higher is recommended. For footings and foundations, M15 (1:2:4) is the minimum. The mix ratio numbers refer to the volume proportion of cement:fine aggregate:coarse aggregate. Higher cement content gives stronger but more expensive concrete.
How much water should be added to concrete mix?
The water-cement (W/C) ratio is crucial to concrete strength. A lower W/C ratio gives higher strength. Standard ratios: M20 concrete uses approximately 0.50-0.55 W/C ratio. M25 uses 0.45-0.50. Too much water weakens the concrete (dilutes the cement paste) and increases shrinkage cracking. Too little makes the mix unworkable. Use the minimum water needed to achieve proper workability. A slump test (100-150 mm for general use) is the field test for workability.
What is the water-cement ratio and why does it matter?
The water-cement (W/C) ratio is the mass of water divided by the mass of cement in a mix. A lower W/C ratio produces stronger, more durable concrete (typical structural concrete uses 0.45-0.55). Excess water creates capillary pores that weaken the hardened concrete and increase shrinkage cracking. For every 0.1 increase in W/C ratio above 0.4, compressive strength can drop by 5-10 MPa. Always use the minimum water needed for workability, and never add extra water to a mix on-site without recalculating cement content.
What is the difference between M20 and M25 concrete?
M20 has a characteristic compressive strength of 20 MPa at 28 days; M25 has 25 MPa. M20 is used for slabs, beams, and columns in residential construction. M25 is used for heavier structural elements and high-rise buildings. Higher M-grade requires more cement and a lower water-cement ratio.