The free comman can be used to show the free and used memory on both RAM and Swap files.
Sample Usage
List Free and Used Memory in Either Kilobytes, Megabytes or Gigabytes
Kilobytes
free -k
# or
free -kilo
Megabytes
free -m
#
free --mega
Gigabytes
free -g
# or
free --giga
Show List in Human Readable Format
free -h
# or
free --human
