Concrete Grade (M20, M25…)
Also known as: grade of concrete, M20, characteristic strength
Concrete grade denotes its characteristic compressive strength in N/mm² at 28 days, written as M followed by the strength.
A grade like M20 means concrete with a characteristic compressive strength of 20 N/mm² at 28 days (the 'M' stands for mix). Common structural grades are M20, M25, and M30; leaner grades such as M10 and M15 are used for blinding and non-structural work.
Each grade corresponds to a nominal or design mix of cement, sand, and coarse aggregate. M20, for example, is the IS 456 nominal mix 1 : 1.5 : 3. Higher grades carry more load and improve durability and bond, which is why development and lap lengths shorten as the grade rises.
Choosing the right grade balances strength, durability, and cost for each member of the structure.