How can we calculate the actual size of MPEG file which will be crated?

If you choose CBR, The following equation can be used to calculate. "2048/2018" stands for bitrate of system stream.

Filesize (Kb) = (Video+Audio) x (2048/2018) x sec/8

E.g. Video is 1150Kbps, audio is 224Kbps, 15 sec MPEG file would be "(1150+224) x (2048/2018) x 15/8" = 2614KB