| Primary value | 1 : 1.5 : 3 C : S : A (≈ 390 kg cement per m³ · M15 1:2:4 · M25 designed mix) |
| Applies to | Site-mixed nominal-mix RCC concrete up to M20 grade · Domestic and small-project site batching · Estimation of cement / sand / aggregate quantities per cum |
| Exceptions | M5 — lean concrete (PCC) → 1 : 5 : 10 |
| M7.5 → 1 : 4 : 8 | |
| M10 (PCC under footing) → 1 : 3 : 6 | |
| M15 → 1 : 2 : 4 | |
| M20 (RCC residential) → 1 : 1.5 : 3 | |
| M25 and above → Designed mix only — not nominal | |
| Measured as | Volumetric ratio of cement : fine aggregate (sand) : coarse aggregate (stone), measured by farma boxes or mechanical batching. Water added separately to achieve target slump. |
| Source | IS 456 — Clause 9.1, Table 9 ✓ Verified |
71 related items across IS codes, knowledge articles, design rules, maps and tools
Nominal mix proportions are the BIS-defined volumetric ratios that small sites use without a dedicated mix-design report. Above M20, IS 456 mandates designed mixes (calculated from cement strength + aggregate gradation) because nominal proportions become unreliable. M20 1:1.5:3 is the universal reference all RCC residential design defaults to.
Site-mix concrete uses 1-bag-cement + 1.5 farma-sand + 3 farma-aggregate per batch (1 farma ≈ 1 cubic foot ≈ 35 L). M25 and stronger grades come exclusively from RMC plants where designed mix is the norm. Most apartment construction now uses M25 RMC for slabs / beams / columns and M20 site-mix only for plinth / lean works.