How the quantities are calculated
Cement weight is computed using its bulk density of 1,440 kg/m³. Sand bulk density ≈ 1,600 kg/m³ and 20 mm coarse aggregate ≈ 1,500 kg/m³ — values vary slightly by source, so order with a 5–10% buffer.
Standard nominal mixes
| Grade | Ratio (Cement : Sand : Agg.) | Typical use |
|---|---|---|
| M15 | 1 : 2 : 4 | PCC, leveling courses, non-structural |
| M20 | 1 : 1.5 : 3 | Most slabs, beams, columns in residential |
| M25 | 1 : 1 : 2 | Heavy-load slabs, columns, retaining walls |
For grades M30 and above, design mixes (not nominal) are required — consult IS 10262 for proportioning.
FAQ
Does this include water?
No. Water-cement ratio is typically 0.45–0.55 by weight depending on workability and grade. For 1 cu.m of M20, that's about 180–200 litres of water on top of the cement.
What about wastage?
The 1.54 factor accounts for void filling but not for spillage on site. Add 3–5% to the bag count for handling losses on small jobs and 1–2% on large, well-managed projects.
Is M20 the same as 1:1.5:3?
1:1.5:3 is the nominal volume ratio. M20 means a characteristic compressive strength of 20 N/mm² at 28 days. They're equivalent for nominal-mix design but the strength target governs in design-mix concrete.