The mix proportions for M20 & M25 both, shall be designed
by laboratory trials and designed according to BIS 10262,
383 & 456 or SP 23. The ratio 1:1.5:3 was given earlier in
IS 456 but IS 456 (2000) does not recommend volumetric
batch for even M20 and hence both should be designed as per
requirement, i.e. it depends on the type of cement,
gradation of aggregates,workability required and
importantly the water cement ratio.

M10 manual mix, proportion is 1:3:6(C:FA:CA)
M15 manual mix, proportion is 1:2:4

> M15 are design Mix, and proportion on Weight basis (not by
volume basis) depend upon grade/type of cement, type of fine
aggregate and Coarse aggregate

However for the estimate purpose the cement can be calculated
For M15 (1:2:4)– cement is 6.37 bags/Cum
M20(1:1.5:3) Cement -8.09 bags/Cum
M25 (1:1:2)cement -12.2 bags/Cum