Cement & Concrete Calculator
Work out how many 50 kg cement bags your concrete needs, along with the sand and aggregate, using standard Indian mix ratios and the industry dry-volume factor.
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Material split by volume
Assumptions used: dry volume factor 1.54 × wet volume; one 50 kg cement bag occupies 0.0347 m³; sand density 1,600 kg/m³; aggregate density 1,500 kg/m³; 5% wastage added to the bag count. These are stored as editable constants in our code.
Why dry volume is larger than wet volume
When cement, sand and aggregate are mixed with water, the fine particles fill the voids between the coarse ones and the mixture shrinks. To produce a given volume of finished concrete you therefore need a larger volume of dry material. The industry standard multiplier is 1.54, and this calculator applies it automatically.
Step by step
- Wet volume — your area × thickness, converted to cubic metres.
- Dry volume — wet volume × 1.54.
- Cement volume — dry volume × (cement part ÷ sum of all parts). For a 1:2:4 mix the sum is 7, so cement takes 1/7th.
- Bags — cement volume ÷ 0.0347 m³, the loose volume of one 50 kg bag. A 5% wastage allowance is then added and the result rounded up.
Which mix ratio should you use?
| Grade | Ratio | Typical use |
|---|---|---|
| M20 | 1 : 1.5 : 3 | Slabs, beams, columns in ordinary residential work |
| M15 | 1 : 2 : 4 | General RCC, footings, small structural members |
| M10 | 1 : 3 : 6 | Plain cement concrete, levelling courses |
| M7.5 | 1 : 4 : 8 | Mass concrete, filling and bedding |
| M5 | 1 : 5 : 10 | Lean concrete under foundations |
Anything structural should be designed by a qualified structural engineer, who may specify a design mix rather than a nominal ratio. Use nominal mixes for small, non-critical work only.
Practical notes
- Order slightly extra. Site wastage, spillage and over-excavation all consume material. A 5% allowance is built in; add more for difficult sites.
- Store cement dry and off the ground. Bags older than about three months, or exposed to damp, lose strength.
- Water matters as much as cement. Adding extra water to make concrete easier to place reduces its strength sharply. Use a plasticiser instead if workability is a problem.
- Cure properly. Concrete gains most of its strength in the first 7–14 days and must be kept damp throughout.
Cement Calculator — common questions
Short, practical answers to the questions people ask most about this tool.
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