M20 Grade:RATIO IS 1:1.5:3

then volume is 1+1.5+3=5.5 and the total volume 

for using mix=1.57 m³ then cement required=1/ 5.5 x 1.57 

=0.285m³ x 1440=411 kg. (8+bag)

sand requried=1.5/5.5 x 1.57=0.471 m³

aggregate required=3/5.5 x 1.57=0.853m³

the standard volume of dry mix mortar=1.57.. 

U can check it in IS code also. 

Then volume is 

1+1.5+3=5.5 and the total volume for using 

mix=1.57 m³ then cement required =1/ 5.5 x 1.57

=0.285 m³ x 1440=411 kg.(8+bag) 

sand requried=1.5/5.5 x 1.57=0.471 m³

aggregate required=3/5.5 x 1.57=0.853 m³

the standard volume of dry mix mortar=1.57..