Accurate calculation of memory utilization in Linux

Hi, We use ps aux | awk '{sum +=$4}; END {print sum}' to find the total memory utilization excluding the buffers and cache. This one manipulates the wrong data at some instances. No idea why  . So in addition to this we can adopt the below commands as wel.. free -m | grep "+" | awk {'print $3/$4*100'} or more handy U=`free -m | grep "+" | awk {'print $3'}`;F=`free -m | grep "+" | awk {'print $4'}`;echo "scale=2;$U/$F*100"| bc There may be another ways as well. Comments please.