M20 vs M25 Concrete: Difference, Mix Ratio and Where to Use
M20 vs M25 concrete: the number is the characteristic compressive strength in N/mm² (MPa) of 150 mm concrete cubes tested at 28 days. M20 must reach 20 N/mm² and M25 must reach 25 N/mm². M20 is the minimum grade IS 456 allows for RCC in mild exposure and can be made as a nominal mix of about 1:1.5:3. M25 is required for moderate exposure, which includes footings buried in soil, and must be made as a design mix, not a volume ratio. M25 has a lower water-cement ratio, so it is denser and more durable.
Structural drawings for Indian houses usually say “M20” or “M25” for each element, and contractors and ready-mix suppliers quote by grade. The five-point difference sounds small, but it changes how the concrete must be mixed, how much water is allowed and where it can be used. This guide explains what the grades mean, the IS 456 rules behind them, and which one to use where.
Last updated: 24 October 2026
M20 vs M25: quick comparison
| Factor | M20 | M25 |
|---|---|---|
| Characteristic strength (28-day cube) | 20 N/mm² | 25 N/mm² |
| Group in IS 456 (Table 2) | Ordinary concrete (M10–M20) | Standard concrete (M25–M55) |
| How it may be made | Design mix, or nominal mix of about 1:1.5:3 | Design mix only |
| Minimum grade for RCC in | Mild exposure | Moderate exposure |
| Max water-cement ratio (RCC) | 0.55 (mild) | 0.50 (moderate) |
| Min cement content (RCC) | 300 kg/m³ | 300 kg/m³ |
| Nominal cover (IS 456 Table 16) | 20 mm (mild) | 30 mm (moderate) |
| Typical use in houses | Slabs, beams and columns in protected, non-coastal conditions | Footings in soil, exposed elements, larger spans, many ready-mix pours |
| Durability | Adequate for mild exposure | Denser, less permeable |
| Cost | Lower | Somewhat higher (more control, often more cement or admixture) |
What does “M20” mean?
“M” stands for mix, and the number is the characteristic compressive strength in N/mm² of 150 mm cubes at 28 days. “Characteristic” means that no more than 5% of test results are expected to fall below that value. So a correctly produced M20 concrete has an average strength well above 20, and only a small share of cubes should come close to 20.
The grade is about concrete, not cement. The 43 or 53 grade on a cement bag is a different test; see OPC vs PPC cement.
Nominal mix vs design mix: the key difference
A nominal mix uses fixed proportions by volume, such as 1:1.5:3 (cement : sand : coarse aggregate). It is simple and still common on small house sites. IS 456 allows nominal mixes only for M20 and lower grades.
A design mix is worked out for the actual cement, sand, aggregate and target workability, following IS 10262, and is confirmed with trial cubes. Proportions are set by weight, the water is controlled, and an admixture is often used. M25 and above must be design mixes. A ratio like 1:1:2 is sometimes quoted for M25 on site, but it is only a rough guide and does not meet IS 456 for M25.
In practice, the easiest way to get a true M25 on a house project is ready-mix concrete (RMC) from a plant that supplies its mix design and cube results.
| Grade | Typical nominal mix (by volume) | Allowed as nominal mix? |
|---|---|---|
| M7.5 | 1 : 4 : 8 | Yes (PCC) |
| M10 | 1 : 3 : 6 | Yes (PCC) |
| M15 | 1 : 2 : 4 | Yes |
| M20 | 1 : 1.5 : 3 | Yes (upper limit) |
| M25 | Design mix | No |
For where the lower grades are used, see PCC vs RCC.
Exposure conditions: why footings may need M25
IS 456 sets the minimum grade by how harsh the surroundings are. In simplified terms:
- Mild (M20 minimum): concrete protected from weather and aggressive conditions, except in coastal areas. For example, interior slabs, beams and columns.
- Moderate (M25 minimum): concrete sheltered from severe rain, exposed to condensation and rain, buried in non-aggressive soil, or continuously under water. This includes most footings and foundations.
- Severe (M30 minimum): alternate wetting and drying, severe rain or freezing, or a coastal environment.
So a house may correctly use M20 for its superstructure and M25 for its foundations, or M25 throughout for simplicity. Near the sea, the minimum rises to M30. Your structural engineer decides the exposure class for each element.
Which grade for which part of the house?
| Element | Commonly specified | Reason |
|---|---|---|
| PCC bed under footings | M7.5 or M10 | Levelling course, not structural |
| Footings, plinth beams | M25 | In contact with soil: moderate exposure |
| Columns | M20 or M25 | Depends on exposure, load and number of floors |
| Beams and slabs | M20 or M25 | M25 is common with ready-mix and for larger spans |
| Roof slab and exposed chajja | M25 | Exposed to rain and sun |
| Water tanks | M25 or higher | Continuously wet; needs low permeability |
| Coastal houses | M30 or higher | Severe exposure |
This reflects common practice. The grade on your structural drawing always takes precedence.
How the grade is checked: cube tests
During a pour, samples of concrete are cast into 150 mm cube moulds, cured in water and crushed at 7 and 28 days. The 28-day result is what the grade refers to; 7-day results give an early warning. IS 456 sets acceptance rules based on groups of results, not a single cube. If you buy ready-mix, ask the supplier for the cube results for your batch, and on a site-mixed pour, ask the contractor to cast cubes.
Workability is checked on site with a slump test. Adding water to raise the slump lowers the strength, which is the most common way an M25 order ends up performing like a lower grade. For more, see workability of concrete.
How much cement in M20?
For a nominal 1:1.5:3 mix, a common rule of thumb is to take the dry volume as about 1.54 times the wet volume. One cubic metre then needs about 1.54 ÷ 5.5 = 0.28 m³ of cement. At about 1,440 kg/m³ that is roughly 400 kg, or 8 bags of 50 kg. A design-mix M25 may use a similar or somewhat different amount of cement depending on materials and admixture. The mix design sheet gives the actual figure. To estimate quantities for a pour, use the concrete volume calculator.
Common mistakes
- Ordering “M25” but mixing it by volume on site with no design or cube tests.
- Adding water at the site to make pumping or placing easier.
- Using M20 for footings in soil, or for coastal work, where IS 456 calls for a higher grade.
- Reducing cover to save concrete; the cover is part of durability, not decoration.
- Skipping cube tests, which leaves no record of what was actually poured.
- Short curing; strength and durability both depend on it.
Hindi terms used on site
Grades are spoken as “M-twenty” and “M-pachees” (M25) or simply “20 grade” and “25 grade”. Cement, sand and aggregate are सीमेंट (cement), रेत (ret) and गिट्टी (gitti); a mix of 1:1.5:3 is described as “ek-dedh-teen ka masala”. Cube testing is often called “cube bharna” (casting cubes).
FAQ
What is the difference between M20 and M25 concrete?
M20 has a characteristic 28-day cube strength of 20 N/mm² and M25 has 25 N/mm². M20 may be made as a nominal volume mix (about 1:1.5:3); M25 must be a design mix with a lower water-cement ratio, which makes it denser and more durable.
What is the mix ratio of M25 concrete?
M25 has no permitted nominal ratio under IS 456; it must be designed to IS 10262 for the actual materials. Ratios like 1:1:2 are only rough site rules.
Is M20 enough for a house?
For superstructure elements in mild exposure, yes, M20 is the IS 456 minimum for RCC. Footings in soil fall in moderate exposure, which needs M25, and coastal sites need M30 or higher.
How many bags of cement are in 1 m³ of M20?
About 8 bags of 50 kg for a nominal 1:1.5:3 mix, using the common 1.54 dry-volume factor. Design mixes vary.
What is the 7-day strength of M20?
Concrete with OPC typically reaches roughly two-thirds of its 28-day strength in 7 days, but this varies with cement type, temperature and curing. PPC gains more slowly. Use 7-day results only as an early indication.
Related guides: PCC vs RCC · RCC full form · OPC vs PPC cement · Ready mix concrete · All construction guides
Disclaimer: Educational only. Concrete grade, exposure class, mix design, cover and acceptance testing must follow your structural drawings, IS 456 and IS 10262, as specified by a qualified engineer. Disclaimer
Tanmay Arora, is an Architect with an experience of 13+ years. He is a Management Grad with a post Graduate Diploma in Building Construction and Materials. Tanmay has worked with renowned firms. He has graduated in Bachelor of Architecture. His deep interest in Architecture and Civil Engineering and his experience has made him one of the best architects a client can think of.
