The ratios for M20, M25, and M30 concrete are approximately: M20 (1:1.5:3), M25 (1:1:2), and M30 (1:0.75:1.5).

Here's a breakdown:

M20: 1 part cement, 1.5 parts sand, and 3 parts aggregate. 

M25: 1 part cement, 1 part sand, and 2 parts aggregate. 

M30: 1 part cement, 0.75 parts sand, and 1.5 parts aggregate.