From a command shell, use the “concatenate” command: cat /proc/meminfo for memory usage information. You should see a line starting MemTotal: see below. ie: MemTotal: 15733472 or 15GB, MemFree: and MemAvailable:
This is the total memory Linux thinks it has available to use.
You can also use commands
free - m vmstat top htop
to find current memory usage