Concrete Mix Ratio Calculator Formula
Understand the math behind the concrete mix ratio calculator. Each variable explained with a worked example.
Formulas Used
Cement Volume
cement_vol = dry_vol * cement_ratio / total_partsCement (50 kg bags)
cement_bags = dry_vol * cement_ratio / total_parts * 1440 / 50Sand Volume
sand_vol = dry_vol * sand_ratio / total_partsAggregate Volume
aggregate_vol = dry_vol * aggregate_ratio / total_partsVariables
| Variable | Description | Default |
|---|---|---|
volume | Concrete Volume Needed(m^3) | 1 |
cement_ratio | Cement Part | 1 |
sand_ratio | Sand Part | 2 |
aggregate_ratio | Aggregate Part | 4 |
dry_factor | Dry Volume Factor | 1.54 |
total_parts | Derived value= cement_ratio + sand_ratio + aggregate_ratio | calculated |
dry_vol | Derived value= volume * dry_factor | calculated |
How It Works
Concrete Mix Design by Ratio
A mix ratio specifies the proportional volumes of cement : sand : aggregate.
Method
1. Dry volume = Wet volume x 1.54 (factor accounts for voids and compaction) 2. Divide dry volume by sum of ratio parts 3. Multiply each ratio part by the unit volume 4. Convert cement volume to bags: volume x 1440 kg/m^3 (bulk density) / 50 kg per bag
Common ratios: 1:2:4 for M15 (general purpose), 1:1.5:3 for M20 (structural), 1:1:2 for M25 (high strength).
Worked Example
1 m^3 of concrete at 1:2:4 ratio.
volume = 1cement_ratio = 1sand_ratio = 2aggregate_ratio = 4dry_factor = 1.54
- 01Dry volume = 1 x 1.54 = 1.54 m^3
- 02Total parts = 1 + 2 + 4 = 7
- 03Cement = 1.54 x 1/7 = 0.220 m^3 = 0.220 x 1440 = 316.8 kg = 6.3 bags
- 04Sand = 1.54 x 2/7 = 0.440 m^3
- 05Aggregate = 1.54 x 4/7 = 0.880 m^3
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