Why this calc exists
Nominal mix is the older, simpler way of prescribing concrete — by ratio rather than by design. IS 456 Cl 9.3 limits it to M20 or lower because beyond that, the strength scatter becomes too wide for structural reliability. But for non-structural blinding, foundations of single-storey buildings, and site levelling, nominal mix is faster and cheaper.
The catch is that the table values are mass-based, not volume-based. Table 9 gives dry aggregate mass per 50 kg of cement, plus max water per 50 kg. The commonly-quoted '1:2:4' and '1:3:6' ratios are mass-ratio shorthand. The Nominal Mix calculator applies Table 9 to your project volume and gives cement bags, sand m³, CA m³, and water L — directly usable at site.
Code references (with provenance)
- IS 456 Cl 9.3 — Nominal mix may be used for M20 or lower grades; mass basis from Table 9.
- IS 456 Cl 9.3.1 — Mix proportions by mass; water per 50 kg cement as in Table 9; FA:CA ratio adjusted for grading/MSA.
- IS 456 Cl 9.3.2 — For M20 design mix required where durability, exposure, or structural reliability demand tighter control.
- IS 10262 — Design mix method (for M25 and above).
Table 9 (kg aggregate / 50 kg cement, max water)
M5 — 800 kg · 60 L
M7.5 — 625 kg · 45 L (PDF wins over the 640 kg some web sources quote)
M10 — 480 kg · 34 L
M15 — 380 kg · 32 L
M20 — 320 kg · 30 L
For Zone II sand and MSA 10/20/40 mm the canonical ratio examples are: 1:1½:1:2:1:2½ (M5 to M20 progression).
Field notes (what trips people up)
- Mass, not volume. '1:2:4' means 1 kg cement : 2 kg sand : 4 kg CA, not 1 litre : 2 litres : 4 litres. Cement density is 1440 kg/m³ loose, sand ~1500–1700, CA ~1500–1600. The volumetric equivalents are misleading.
- FA:CA ratio adjusts by zone. Coarser sand (Zone I) wants more FA; finer sand (Zone IV) wants less. IS 456 Table 9 commentary gives 1:1½ (upper) to 1:2½ (lower) — adjust ±0.5 by zone.
- M20 is the ceiling. Don't push nominal mix to M25 or M30 — the strength scatter (typically CoV 18–22 % for nominal vs 12–15 % for design mix) makes it uneconomical and unreliable.
- Admixtures not addressed. Table 9 is plain OPC + sand + CA + water. If you need plasticiser, retarder, or SCM, switch to design mix per IS 10262.
Worked example
Site: 10 m³ of M15 nominal mix in a non-structural foundation strip.
Inputs: Zone II sand, MSA 20 mm.
Output: cement 50 × 10 = 500 bags (typical 5 bags/m³ at M15) · sand 9.5 m³ loose · CA 19.0 m³ loose · water 1,600 L.
Ratio check: 1 : 1.9 : 3.8 — within the 1:2:4 shorthand band for M15 (the table says 380 kg agg per 50 kg cement, so 50 × 7.6 = 380 kg aggregate per bag, split ~127 sand + 253 CA; that's 1:1.9:3.8 by mass).
FAQ
Can I use nominal mix for M25?
No. IS 456 Cl 9.3 caps it at M20. For M25 and above, design mix per IS 10262 is mandatory.
Why does the table use mass instead of volume?
Volume is sensitive to loose bulk density (which varies with moisture, compaction, particle shape). Mass is a stable, reproducible reference. Volumetric ratios on site assume a known gauge box and consistent shovel technique — they introduce 10–15 % extra scatter.
What about water?
Water is the most sensitive component. Table 9 caps water per 50 kg cement; field practice adjusts for aggregate moisture (sand can carry 5–8 % by mass of free water in monsoon).
Related reading & tools
Indicative tool — not a substitute for engineering judgement.
Results are computed from formulae and reference values cited to Indian Standards and other published codes as named on this page, using nominal default assumptions; clause and table references are given in good faith for study and preliminary checks. Always verify the current edition and amendments of any cited standard in the BIS catalogue before relying on it. Final mix proportions, structural checks and construction decisions must be confirmed by a qualified engineer against the project design brief, drawings and site conditions. ConcreteInfo accepts no liability for design, procurement or construction decisions taken on the basis of these tools. Code references & rights: Indian Standards are the property of the Bureau of Indian Standards (© BIS) — official PDFs at bis.gov.in. Shared in good faith as technical reference for the civil engineering fraternity — always verify against the official publication.