Grade of concrete is defined as the minimum strength the concrete must posses after 28 days of construction with proper quality control. Grade of concrete is denoted by prefixing M.
The higher the number the harder it gets. Below are some of the commonly used grades for small scale construction.
These grade of concrete is converted into various mix proportions. For example, for M20 concrete, the mix proportion will be 1:1.5:3 for cement : sand: coarse aggregates.
The most common grades of concrete are M15 for plain cement work and M20, M25 for reinforced concrete construction.