Grades Of Concrete In IS 456 1978 the different grades of concrete are given as M10 M25 M20 M25 M30 M35 and M40 In the classification of concrete mix the letter M denotes the Mix and the numbers 10 15 20 25 30 35 40 represent the predetermined works cube strength of 15 cm cubes after curing of 28 days in N mm2 …