free [options]

Display statistics about memory usage: total free, used, physical, swap, shared, and buffers used by the kernel.

Linux Commad Options:
-b Calculate memory in bytes.
-k Default. Calculate memory in kilobytes.
-m Calculate memory in megabytes.
-o Do not display “buffer adjusted” line. The -o switch disables the display “-/+ buffers” line that shows buffer memory subtracted from the amount of memory used and added to the amount of free memory.
-s time
Check memory usage every time seconds.
-t Display all totals on one line at the bottom of output.
-V Display version information.

Examples:

 free -m      Show amount of (remaining) RAM (-m displays in MB)