Concrete strength measured using concrete cubes produce a results different than concrete cylinders. Conservative estimates put concrete cylinders at 80% of concrete cubes, for high-strength concrete some say the percentage is near 100%.

The ratio between the cube(150mm) and cylindrical sample(150×300 mm).

Generally Strength of Cylinder sample= 0.8 x Strength of Cube. Example:- M20 is equivalent to C25

C25 is 1:1.5:3(1 part cement, 1.5parts fine aggregate, and 3 parts coarse aggregate.)

where as C25 symbolizes aCylindrical sample in which cement, fine aggregates, coarse aggregates are mixed in such a ratio that its characteristic compressive strength is 25 N/mm^2 after 28 days of curing.

M 20 is 1:1.5:3

where as M20 symbolizes a Cubic sample in which cement, fine aggregates, coarse aggregates are mixed in such a ratio that its characteristic compressive strength is 20 N/mm^2 after 28 days of curing.