Every nominal mix calculation in India starts by multiplying by 1.54. It looks like a magic number; it is really a correction for the air between particles.
Where the Volume Goes
Take a heap of 20 mm aggregate: roughly 40 percent of it is air between the stones. Pour sand in, and the sand fills much of that air without adding much volume. Add cement, and it fills gaps between sand grains. Add water, and the paste fills the remainder. The result is far denser than the loose heaps you started with.
So to end up with 1 m³ of concrete, you need more than 1 m³ of loose cement, sand and aggregate — about 1.52 to 1.57 m³ by convention, usually taken as 1.54.
Using the Factor
M20 (1 : 1.5 : 3), per m³:
- Dry volume = 1 × 1.54 = 1.54 m³
- Sum of parts = 5.5
- Cement = 1.54 × 1/5.5 = 0.28 m³ = 403 kg = 8.06 bags
- Sand = 1.54 × 1.5/5.5 = 0.42 m³
- Aggregate = 1.54 × 3/5.5 = 0.84 m³
Mortar and Plaster
Mortar has no coarse aggregate, so the void effect is smaller: about 1.27, with some estimators using 1.33 to include wastage. Plaster estimates often add a further 20 percent for uneven surfaces.
| Use | Dry volume factor |
|---|---|
| Concrete (nominal mix) | 1.52 – 1.57, usually 1.54 |
| Cement mortar | 1.27 – 1.33 |
| Plaster | 1.27, plus ~20% for unevenness |
When Not to Use It
Design mixes, including most ready-mix concrete, are specified by weight per cubic metre from trial batches. Use the supplier's or engineer's mix design quantities directly.
The Short Version
1.54 accounts for the air in loose ingredients. Use it (or your chosen convention) consistently for nominal concrete, 1.27–1.33 for mortar, and design-mix weights where you have them.
