.avi file size

[newbiez]

i'm converting .dat to .avi
the dat file size is around 200 mb
i convert it with
vcdgear dat->mpeg and virtualdub 1.5.4 mpeg ->avi
then the size of avi file is around 90-98 mb
is it normal?

my friend said the scale from dat to avi is 1:4
so normally i could have around 50 mb

is it true?

thx for the replies