How it is calculated
Volume: slab = length × width × thickness; column = π × (diameter ÷ 2)² × height; multiplied by count and allowance.
Dry volume = volume × 1.54. Each material = dry volume × its parts ÷ total parts. Cement mass = its volume × bulk density (≈1,440 kg/m³ or 90 lb/ft³). Water = cement × water/cement ratio.
Worked example
Using the calculator’s example values:
- Element type: Slab, base or footing (rectangular)
- Length: 4 m
- Width: 3 m
- Thickness: 10 cm
- Number of identical elements: 1
- Waste allowance: 5%
- Mix: parts cement: 1
- Parts sand: 2
- Parts gravel: 3
- Dry volume factor: 1.54
- Cement bulk density: 1,440 kg/m³
- Cement bag weight: 25 kg
- Water/cement ratio: 0.5
- Price per bag (optional): $0.00
Result: Concrete volume — 1.26 m³ (cement bags: 19 units; cement: 465.7 kg; sand: 0.647 m³).
Money-saving tips
- For large volumes ready-mix is usually worth it.
- Don’t add extra water: it reduces strength.
- Cure the concrete by keeping it moist for the first days.
Frequently asked questions
Which mix ratio should I use?
It depends on the use. 1:2:3 is a common general-purpose DIY mix, but for foundations or structural elements follow the engineer’s specification.
Why multiply by 1.54?
Because when mixed, cement and water fill the gaps between aggregates; you need more dry volume than the finished concrete.
Does it work for pre-mixed bagged concrete?
Use the calculated volume and the yield stated on the pre-mixed bag (volume per bag).
How we calculate and the limits of the results: Methodology.