Grades of Concrete:

Normally concrete is graded into seven grades as M10, M15, M20, M25, M30, M35, and M40. Within the designation of concrete, letter M refers to the mix and the number refers to the specified features compressive strength of 150 mm cube after 28 days curing expressed in N/mm².

Table: Minimum Characteristic Compressive Strength

A material of characteristic compressive strength is the value of the material below which not more than 5% of the test results are expected to fail.