Created on: May 11, 2013
Last updated: August 18, 2020
Unfortunately, there is no one correct answer to this question.
It depends on the specific Mac you're using, the operating system on that Mac, and the specific software applications you use. While Apple lists only 2GB as the requirement for some operating system versions, this is a bare minimum for basic operation. In this scenario, if you run many apps at the same time with only 2GB of RAM, the system responsiveness may slow down.
For that reason, if you want to leave yourself some leeway to use multiple apps at the same time, 4GB is often good minimum starting point, 8GB is better if your computer supports it. If you intend to work with digital audio or video on a regular basis or (for example) the Adobe Creative Cloud suite, you will likely need 16GB or more. Please consult your Mac user manual to determine the total amount of RAM which can be installed, and the developer of your favorite apps to determine their RAM requirements.