Concrete calculator
Cement bags, sand and aggregate for any volume of M10, M15, M20 or M25 concrete, from the nominal mix ratios and the 1.54 dry-volume factor.
Calculate
- Concrete volume
- 1.35 m³ (47.67 cft)
- Mix
- M20, cement : sand : aggregate = 1 : 1.5 : 3
- Cement
- 10.9 bags of 50 kg (544 kg)
- Sand
- 0.567 m³ (20.02 cft)
- Aggregate
- 1.134 m³ (40.05 cft)
How it is calculated
The volume of concrete is length × width × thickness. Dry cement, sand and aggregate take up about 54 % more room than the wet concrete they make, because water and paste fill the voids between grains, so the dry volume is the wet volume × 1.54.
The dry volume is split by the nominal mix ratio: 1 : 1.5 : 3 for M20, for example, is 5.5 parts, of which one is cement. Cement weighs about 1,440 kg per m³, so a 50 kg bag is 0.0347 m³.
Nominal mixes suit small and routine work. Structural concrete for columns, beams and slabs above M20 is normally a design mix from a lab or a ready-mix plant, with its own proportions.
An estimate for ordering material, not a structural design. Your engineer's drawings and site measurements decide the final quantities.
Questions
- How many bags of cement are needed for 1 m³ of M20 concrete?
- About 8 bags of 50 kg for a nominal 1 : 1.5 : 3 mix, with 0.42 m³ of sand and 0.84 m³ of aggregate.
- What are the mix ratios of M15, M20 and M25?
- Nominal mixes of cement : sand : aggregate are M10 1 : 3 : 6, M15 1 : 2 : 4, M20 1 : 1.5 : 3 and M25 1 : 1 : 2.
- Why multiply the volume by 1.54?
- Dry materials shrink in volume once water is added and the paste fills the gaps between grains; 1.54 is the conventional allowance for it.
- How do I convert cubic metres to cubic feet?
- One cubic metre is 35.31 cubic feet. Sand and aggregate are often sold by the cft or by the trolley.