Mostly the ratio of 1:1.5:3 is used for M20 grade of concrete

So, Volume of dry concrete = 1.54 to 1.57 times volume of wet concrete

Assume, 1cum of concrete work ratio sum = 1+1.5+3 = 5.5

shrinkage or safety factor = 1.57

Total volume of wet concrete required is = 1.57cum

Volume of broken stone require = (3/5.5) * 1.57 = 0.856 m3

Volume of sand require = (1.5/5.5) * 1.57 = 0.471 m3

Volume of cement = (1/5.5) * 1.57 = 0.285 m3

=0.285*1440 =411 kg

For 1 m3 of M20 (1:1.5:3)

Broken stone = 0.856 m3

Sand = 0.472 m3

Cement = 8.22 bag

Therefore,

8 bag of cement is required for 1cum of concrete work in M20