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Structural6 min read

Concrete grades —
M10 to M40 explained

Concrete grade determines the compressive strength of your structure. Using a lower grade than required is one of the most common — and dangerous — cost-cutting measures in construction.

1What is grade?2M10–M40 table3Site mix vs RMC4Curing rules5RMC brands6Homekrate picks
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The homeowner's summary

The M in M20 stands for Mix, and the number is the compressive strength in MPa after 28 days of curing. For a standard home in Bengaluru, M20 is the minimum for slabs and M25 is recommended for columns and beams. Never let your contractor use M15 for structural elements — it is not safe. Ready-mix concrete (RMC) from a certified plant is always more consistent than site-mixed concrete.

Grades — M10 to M40

Characteristic compressive strength of 150mm cube at 28 days. Governed by IS 456:2000.

Grade
Mix ratio
Strength
Best use
Recommendation
M10
1:3:6
10 MPa
Plain concrete, levelling course, PCC
Sub-base work only
M15
1:2:4
15 MPa
Plain concrete footings, pathways
Non-structural
M20
1:1.5:3
20 MPa
Slabs, beams, columns — general residential
Basic package minimum
M25
1:1:2
25 MPa
Columns, beams, foundations — quality residential
Standard package
M30
Design mix
30 MPa
High-rise, heavy load structures
Premium package
M35
Design mix
35 MPa
Bridges, industrial, special structures
Specialist use
M40
Design mix
40 MPa
High-rise cores, prestressed elements
Specialist use

↑ M25 row highlighted — our standard recommendation for Bengaluru residential projects.

Site mix vs Ready-mix (RMC)
Site-mixed concrete
Manual batching on site
→Mixed manually or with a small mixer
→Ratio depends on worker judgment — inconsistent
→No quality control or testing
→Acceptable for minor works only
→Never use for M25 and above
Ready-mix concrete
Certified plant — recommended
→Mixed at certified plant with precise proportions
→Consistent grade — tested before dispatch
→Delivered in transit mixers — poured immediately
→Mandatory for M25 and above
→Slump test done on site before pouring
Critical curing rules
01
Cure for minimum 28 days
Concrete gains ~70% strength in 7 days but needs 28 days to reach design strength. Curing means keeping it moist — not just wet on day 1.
02
Never add excess water
Extra water to improve workability is the most common cause of weak concrete. Use admixtures (plasticisers) if workability is needed.
03
Cover within 24 hours
Cover with wet gunny bags or curing compounds within 24 hours of pouring. Exposed concrete dries too fast and develops surface cracks.
04
Do not load too early
Never allow construction loads on slabs before 28 days. Formwork can be removed after 14 days for slabs but full loading must wait 28 days.
Reputed RMC suppliers
Ultratech ConcreteACC ConcreteRMC ReadymixPrism JohnsonSanghi Cement RMCLafarge Holcim

Always ask for the delivery challan with grade, slump and batch number. Insist on a slump test at site before pouring.

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Homekrate specification
Basic
M20 site mix for slabs, M20 RMC for columns
Minimum acceptable for residential. Not recommended for 3+ floors.
Standard
M25 RMC for all structural elements
Our default. Consistent quality, tested grade, suitable for G+2 and G+3.
Premium
M30 RMC for columns/beams, M25 for slabs
For G+4 and above or clients who want the highest structural safety.
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