Concrete Mix Ratio Calculator
Calculate concrete mix ratios of cement, sand, gravel, and water by strength grade.
Returns proportions for M10 to M30 in weight and volume measurements.
Concrete mix ratios define the proportions of cement, sand (fine aggregate), gravel (coarse aggregate), and water needed to achieve a specific strength. Getting the ratio right is essential for structural integrity, workability, and durability.
Standard Mix Ratios by Grade:
| Grade | Ratio (Cement:Sand:Gravel) | Strength (PSI) | Strength (MPa) | Common Use |
|---|---|---|---|---|
| M10 | 1 : 3 : 6 | 1,450 | 10 | Non-structural, leveling |
| M15 | 1 : 2 : 4 | 2,175 | 15 | Pathways, light foundations |
| M20 | 1 : 1.5 : 3 | 2,900 | 20 | General purpose, slabs, beams |
| M25 | 1 : 1 : 2 | 3,625 | 25 | Structural elements, driveways |
| M30 | 1 : 0.75 : 1.5 | 4,350 | 30 | Heavy structural, bridges |
Water-Cement Ratio: The water-cement ratio (w/c) is critical. Too much water weakens concrete; too little makes it unworkable.
| Application | Typical w/c Ratio |
|---|---|
| High strength (M30+) | 0.35–0.40 |
| General purpose (M20) | 0.45–0.50 |
| Non-structural (M10–M15) | 0.50–0.60 |
Formula: Water (liters) = Cement weight (kg) × w/c ratio
Volume Estimation: Working the M20 numbers below backwards, one 50 kg bag of cement makes about 0.124 m³ (4.4 cubic feet) of finished concrete, and a 94 lb (42.6 kg) bag makes about 0.106 m³ (3.7 cubic feet). Those figures move with the mix: a leaner M10 stretches a bag further, a rich M30 uses it up faster.
Calculating Materials per Cubic Meter (M20 mix, 1:1.5:3): Total parts = 1 + 1.5 + 3 = 5.5 parts
- Cement: 1/5.5 × 1.54 (dry volume factor) = 0.28 m³ = 403 kg, so 9 bags of 50 kg with a little left over
- Sand: 1.5/5.5 × 1.54 = 0.42 m³ (~630 kg)
- Gravel: 3/5.5 × 1.54 = 0.84 m³ (~1,260 kg)
- Water: 403 × 0.45 = ~181 liters
Bag counts always round up, because eight and a bit bags means buying nine.
The 1.54 dry volume factor accounts for the volume increase when converting wet (compacted) concrete volume to dry material volume, because air voids in dry materials occupy more space.
Mixing Tips: Always add water gradually. You can always add more, but you cannot take it back out. Mix dry ingredients first, then add water. For small projects, a wheelbarrow and shovel work fine. For anything over 0.5 cubic meters (about 18 cubic feet), consider renting a mixer or ordering ready-mix.
Temperature Considerations: Do not pour concrete when temperatures are below 40 degrees Fahrenheit (4 degrees Celsius) or above 90 degrees Fahrenheit (32 degrees Celsius). Cold weather slows curing; hot weather causes rapid moisture loss and cracking. In hot conditions, keep materials cool and cure with water or wet burlap. In cold conditions, use heated water and insulating blankets.
Curing Time: Concrete reaches about 70% of its final strength in 7 days and 99% in 28 days. Keep it moist for at least 7 days for best results. Never let fresh concrete dry out too quickly.
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