by Nominal mix concrete is prepared using prescribed or conventional proportions of cement, fine aggregate and coarse aggregate without carrying out a laboratory-based trial mix design. Under IS 456:2000, nominal mix concrete may be used for grades M20 or lower, subject to the applicable project requirements.
Although simple to prepare, the strength and durability of nominal mixes can vary depending on the quality of materials, water-cement ratio, batching accuracy, compaction, curing and workmanship.
For modern reinforced concrete construction, design mix concrete is generally preferred because it provides better control over strength, durability and workability.
Page Contents
Standard Nominal Mix Proportions of Concrete
The following table shows commonly used practical nominal mix proportions for grades up to M20. These ratios are provided for practical understanding and should be read together with the requirements of IS 456:2000 Table 9.
| Grade of Concrete | Characteristic Compressive Strength (MPa) | Commonly Used Nominal Proportion (Cement : Fine Aggregate : Coarse Aggregate) | Typical Applications |
|---|---|---|---|
| M5 | 5 | 1 : 5 : 10 | Lean concrete, leveling course, PCC below foundations |
| M7.5 | 7.5 | 1 : 4 : 8 | Bedding concrete, sub-base works, non-structural applications |
| M10 | 10 | 1 : 3 : 6 | Plain cement concrete, flooring base, foundation leveling |
| M15 | 15 | 1 : 2 : 4 | Footpaths, kerbs, PCC works, non-reinforced concrete |
| M20 | 20 | 1 : 1.5 : 3 | Plain concrete and certain small-scale works where nominal mix is permitted |
Important: The above proportions are commonly expressed as volume ratios for practical site understanding. However, IS 456:2000 Table 9 specifies nominal concrete proportions by mass of dry aggregates and gives the corresponding maximum water quantity per 50 kg of cement. The actual proportions and batching method should follow the applicable project specification and standard requirements.
Why Is M25 Not Included in the IS 456 Nominal Mix Table?
M25 is not included in the nominal mix provisions of IS 456:2000. Clause 9.3 permits nominal mix concrete for grades M20 or lower, and Table 9 provides the corresponding nominal-mix requirements. Therefore, a fixed proportion such as 1 : 1 : 2 should not be presented as an IS 456 nominal mix for M25. For M25 and higher grades, an appropriate design mix should be adopted in accordance with the project requirements and applicable standards.
For higher grades where design mix concrete is required, you can also refer to our M20 Concrete Mix Design and other grade-specific mix design guides.
What Does the Concrete Grade Mean?
The letter “M” in the concrete grade stands for Mix, and the number indicates the characteristic compressive strength of concrete in MPa (N/mm²) after 28 days of curing.
The characteristic compressive strength is specified at 28 days for the standard concrete grades referred to in IS 456.
For example:
- M20 indicates a characteristic compressive strength of 20 MPa after 28 days.
- M25 indicates a characteristic compressive strength of 25 MPa after 28 days.
- M30 indicates a characteristic compressive strength of 30 MPa after 28 days.
The concrete grade helps engineers select the appropriate concrete based on structural requirements, loading conditions, exposure environment, and durability requirements.
Understanding Nominal Mix Proportions
A nominal mix ratio consists of three numbers representing the quantities of cement, fine aggregate, and coarse aggregate.
For example:
M20 Concrete (1 : 1.5 : 3)
This means:
- 1 Part Cement
- 1.5 Parts Fine Aggregate (Sand)
- 3 Parts Coarse Aggregate
Want to calculate the required cement, sand and aggregate quantity for concrete? Use our Cement, Sand & Aggregate Calculator for quick quantity estimation.
Similarly,
M15 Concrete (1 : 2 : 4)
This consists of:
- 1 Part Cement
- 2 Parts Sand
- 4 Parts Coarse Aggregate
On site, these proportions are based on volume batching and should not be confused with weight batching used in design mix concrete.
The ratios such as 1 : 1.5 : 3 are commonly used practical expressions of nominal mix proportions. However, the complete requirements of IS 456 Table 9 are specified in terms of the mass of dry aggregates per 50 kg of cement, the proportion of fine aggregate to coarse aggregate by mass, and the maximum quantity of water. Therefore, these simple ratios should not be treated as a substitute for the complete requirements of Table 9
Nominal Mix vs Design Mix Concrete
| Parameter | Nominal Mix | Design Mix |
|---|---|---|
| Mix Proportion | Prescribed/conventional proportion | Determined through mix design |
| Basis | Standard/proportional requirements and conventional practice | Laboratory trials and engineering calculations |
| Strength Control | More variable | Better controlled |
| Quality Control | Basic to moderate | More rigorous |
| Economy | Less optimized | Can be optimized |
| Durability | Depends strongly on materials and workmanship | Can be designed for required performance |
| Workability Control | More limited | Better controlled |
| Suitable for | M20 or lower where nominal mix is permitted | Structural works and higher grades |
For a detailed explanation of laboratory-based concrete proportioning, target mean strength, water-cement ratio, aggregate selection and mix calculations, see our Concrete Mix Design Guide
Which Concrete Grades Generally Use Nominal Mix?
| Concrete Grade | Nominal Mix under IS 456:2000 | Design Mix |
|---|---|---|
| M5 | ✅ Permitted | ✅ Can be used |
| M7.5 | ✅ Permitted | ✅ Can be used |
| M10 | ✅ Permitted | ✅ Can be used |
| M15 | ✅ Permitted | ✅ Can be used |
| M20 | ✅ Permitted | ✅ Preferred where improved quality control and consistency are required |
| M25 | ❌ Not covered under nominal mix provision | ✅ Generally used |
| M30 | ❌ Not covered under nominal mix provision | ✅ Used |
| M35 | ❌ Not covered under nominal mix provision | ✅ Used |
| M40 | ❌ Not covered under nominal mix provision | ✅ Used |
| M45 | ❌ Not covered under nominal mix provision | ✅ Used |
| M50 | ❌ Not covered under nominal mix provision | ✅ Used |
| M55 | ❌ Not covered under nominal mix provision | ✅ Used |
| M60 | ❌ Not covered under nominal mix provision | ✅ Used |
Note: IS 456:2000 Clause 9.3 permits nominal mix concrete for M20 or lower. For M25 and higher grades, the concrete should be proportioned using an appropriate design procedure in accordance with the project requirements and applicable standards.
Advantages of Nominal Mix Concrete
Nominal mix concrete offers several practical advantages, especially for small projects and low-strength applications.
Advantages
- Simple and easy to prepare.
- Does not require laboratory mix design.
- Suitable for small construction projects.
- Convenient where quality control facilities are limited.
- Faster batching and production.
- Lower initial mix-design effort and cost.
Limitations of Nominal Mix Concrete
Despite its simplicity, nominal mix concrete has several limitations.
Limitations
- Strength may vary due to material quality.
- Higher material consumption than optimized design mixes.
- Less economical for large projects.
- Limited control over workability.
- Lower consistency compared to design mix concrete.
- Not recommended for high-strength structural concrete.
Practical Site Recommendations
To obtain better-quality nominal mix concrete:
- Use clean and properly graded aggregates.
- Measure materials accurately.
- Maintain the specified water-cement ratio.
- Avoid adding excess water during mixing.
- Compact concrete properly using suitable vibrators.
- Start curing as early as practical after finishing.
- Use fresh cement and clean potable water.
Important Engineering Note
A nominal mix proportion does not guarantee that the concrete will achieve the specified grade. The actual compressive strength depends on several factors, including material quality, water-cement ratio, batching accuracy, mixing, transportation, placement, compaction, curing, and workmanship. For important structural members, an approved design mix should always be used in accordance with project specifications and applicable standards.
IS 456 Table 9 — What the Nominal Mix Requirements Actually Specify
| Grade | Maximum Dry Aggregate per 50 kg Cement | Maximum Water per 50 kg Cement |
|---|---|---|
| M5 | 800 kg | 60 L |
| M7.5 | 625 kg | 45 L |
| M10 | 480 kg | 34 L |
| M15 | 330 kg | 32 L |
| M20 | 250 kg | 30 L |
These values come from Table 9 of IS 456:2000.
Important: IS 456 Table 9 does not prescribe one fixed fine-to-coarse aggregate ratio for every nominal mix. The proportion is generally taken as 1 : 2 by mass, but it may vary between 1 : 1.5 and 1 : 2.5, depending on the grading of the fine aggregate and the maximum size of coarse aggregate. As the fine aggregate becomes finer and the maximum size of coarse aggregate becomes larger, the proportion should be adjusted progressively toward the lower limit. Graded coarse aggregate should be used.
Practical Meaning of Table 9
Table 9 gives the maximum total quantity of dry fine and coarse aggregates and the maximum water quantity for every 50 kg of cement. For example, for M20 nominal concrete, the maximum total dry aggregate quantity is 250 kg for every 50 kg of cement, and the maximum water quantity is 30 litres for every 50 kg of cement. The fine and coarse aggregate quantities within this total are adjusted according to the grading of the fine aggregate and the maximum size of coarse aggregate specified in Table 9.
This means that the commonly quoted 1 : 1.5 : 3 ratio should be understood as a practical conventional expression and not as a complete substitute for the requirements of IS 456 Table 9.
Once the concrete volume is known, you can estimate the required concrete quantity for slabs, beams, columns and footings using our Concrete Volume Calculator.
Frequently Asked Questions (FAQs)
1. Is M20 a nominal mix?
Traditionally, M20 has often been produced using a nominal proportion of 1 : 1.5 : 3. However, for projects requiring better quality control and consistent performance, a design mix is generally preferred.
2. Why is M25 generally produced using a design mix?
M25 concrete is commonly used in reinforced concrete structures where higher strength, durability, and consistency are required. Laboratory-designed mixes provide better control over these properties than fixed nominal proportions.
3. Can higher-grade concrete be prepared using nominal mix?
Higher-grade concretes such as M25, M30, M35, M40, and above are generally produced using design mix because fixed nominal proportions cannot reliably achieve the required performance.
4. Is M25 a nominal mix of 1:1:2?
A 1 : 1 : 2 proportion is sometimes quoted as a traditional or empirical M25 ratio in older construction references and online sources. However, it should not be presented as the M25 nominal mix specified by IS 456:2000. IS 456 Clause 9.3 covers nominal mix concrete up to M20. Therefore, M25 should be proportioned using an appropriate design mix procedure where required.
Key Takeaways
- Nominal mix uses prescribed or conventional proportions of cement and aggregates.
- It is suitable mainly for lower-strength and small-scale applications.
- Design mix provides better strength, durability, workability, and consistency.
- M25 and higher grades are generally produced using laboratory-designed concrete mixes.
- Proper batching, water-cement ratio, compaction, and curing are essential to achieve the desired concrete performance, regardless of the mix type.
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