memory calculation

hi all,

sorry for silly question.
but i have a doubt in calculation of memory utilization calculation.

using 'free' command we calculate the memory utilization as
used/total.

but my friend said that its wrong and we have to include cached also as
(used-cached)/memory.

but these gives us much variation between our calculation and this. we totally in confusion about it.....

pleae help me out.

Tanks in advance.