The two methods
This tool offers two ways to estimate material, because they give slightly different bag counts and both are legitimate:
1. Nominal (volumetric) method — default
The method every Indian site engineer learns. Dry volume is the wet concrete volume multiplied by a bulking factor, then split by the mix ratio:
dry volume = wet volume × 1.54
material = (its ratio part / total parts) × dry volume
For M20 (1:1.5:3), one cubic metre of wet concrete needs about 0.28 m³ cement, 0.42 m³ sand and 0.84 m³ aggregate.
2. Design (by cement content) method
For procurement accuracy, cement is taken from typical design-mix content per cubic metre (for example, about 345 kg/m³ for M20), and the remaining dry volume is split between fine and coarse aggregate. This usually yields a slightly different — often lower — cement figure than the nominal method.
Constants we use
| Quantity | Value |
|---|---|
| Dry-volume factor (concrete) | 1.54 |
| Cement density | 1440 kg/m³ |
| Cement bag (India standard) | 50 kg = 0.0347 m³ = 1.226 cft |
| Sand bulk density | 1550 kg/m³ (site range 1450–1600) |
| Aggregate bulk density | 1500 kg/m³ (site range 1450–1550) |
| Water-cement ratio (display) | 0.50 |
| 1 m³ | 35.3147 cft |
| 1 brass | 100 cft = 2.83168 m³ |
Mix ratios by grade
| Grade | Ratio (C:S:A) | Total parts |
|---|---|---|
| M5 | 1:5:10 | 16 |
| M7.5 | 1:4:8 | 13 |
| M10 | 1:3:6 | 10 |
| M15 | 1:2:4 | 7 |
| M20 | 1:1.5:3 | 5.5 |
| M25 | 1:1:2 | 4 |
M25 and richer grades are design mixes under IS 456; the 1:1:2 ratio is a widely used approximation only.
Wastage
A wastage allowance (5% by default, editable) is applied to cement before rounding up to whole bags, reflecting real site loss during handling and mixing.