Let us think the nominal mix is 1:2:4
Loss of cement is considered as 2%
The output of the mix is considered as 67%
To attain 1 cubic meter output, we require 1/0.67 = 1.49 say 1.50 cubic meter dry mix.
Now add the wastage of 2%, i.e (1.50 + 0.02) = 1.52 cubic meter.
Volume of cement = (cement/cement+sand+aggregate) × Total material
=(1/1+2+4) × 1.52
=0.2171 cubic meter
As we know, the density of cement is 1440 kg/cubic-meter and
Weight of 1 bag cement = 50 kg.
Therefore volume of 1 bag cement = 50/1440
=0.0347 cubic meters.
Hence, Numbers of cement bags required in 1 cubic meter = 0.2171/0.0347
= 6.25 bags.
Note: You can use the same formula for calculating cement for other nominal concrete mixes.