The quick answer
For one cubic metre of wet concrete, multiply by 1.54 to get dry volume, then split by the grade's mix ratio. Here are the common grades, per m³, using the nominal method:
| Grade | Cement | Sand | Aggregate |
|---|---|---|---|
| M20 (1:1.5:3) | ~8 bags | 0.42 m³ | 0.84 m³ |
| M15 (1:2:4) | ~6.3 bags | 0.44 m³ | 0.88 m³ |
| M10 (1:3:6) | ~4.4 bags | 0.46 m³ | 0.92 m³ |
| M25 (1:1:2) | ~11 bags | 0.385 m³ | 0.77 m³ |
How the working goes (M20 example)
Total ratio parts for 1:1.5:3 is 5.5. Dry volume of 1 m³ wet concrete is 1 × 1.54 = 1.54 m³.
- Cement = (1/5.5) × 1.54 = 0.28 m³ → 0.28 × 1440 = 403 kg → ~8 bags
- Sand = (1.5/5.5) × 1.54 = 0.42 m³
- Aggregate = (3/5.5) × 1.54 = 0.84 m³
How to use these figures
The per-cubic-metre quantities above are the building block for any concrete estimate. Once you know the wet volume of your element — a slab, beam, column or footing — multiply these per-m³ figures by that volume to get the total cement, sand and aggregate. For example, a 2.5 m³ M20 slab needs roughly 2.5 × 8 = 20 bags of cement, 2.5 × 0.42 = 1.05 m³ of sand and 2.5 × 0.84 = 2.1 m³ of aggregate, before adding a wastage margin.
Why richer grades need more cement
Notice how the cement quantity climbs as the grade rises: M10 needs about 4.4 bags per m³, M20 about 8, and M25 around 11. That is because a higher grade has a larger cement share in its ratio (the "1" part is bigger relative to sand and aggregate), giving a stronger but more expensive mix. The sand and aggregate quantities move in the opposite direction, falling slightly as the mix gets richer. This trade-off is why you match the grade to the job rather than over-specifying: using M25 where M20 suffices wastes cement and money.
Nominal figures vs a real design mix
These quantities come from the nominal-mix method, which splits the dry volume by the fixed ratio. It is accurate enough for estimating and for most residential work up to M20. For M25 and above, IS 456 expects a design mix, where the cement content is calculated and tested for the specific materials — usually giving a slightly different (often lower) cement figure than the nominal approximation. Treat the table above as a procurement guide, not a structural specification for high grades.