What is the meaning of "available RAM" for calculating MySQL max_connections

The question was asked previously, "how do I calculate MySQL max_connections" and this was the answer: > max_connections = (Available RAM - Global Buffers) / Thread Buffers Since I don't have enough reputation to add a comment to the existing question I had to ask a brand new question. I can get the buffer values by executing : SHOW VARIABLES LIKE '%buffer%'; but what is the available RAM part of this equation exactly? Is this value in bytes, kilobytes, megabytes? Something else? Also, do I use the available RAM shown in the resource monitor while my site is being used, or do I need to use the total amount of RAM installed on the machine?