The amount of ram that you use depends on several factors. Size/type of files, number of effects/titles, photos, having other programs open at same time, etc… IMHO there is no one size fits all about ram, but I think now-a-days, 16GB is minimum. If you can afford it, more ram the better/happier, but only if you use it.
You can use Activity Monitor to access your ram usage, both in real time and over a period of time. Wired Memory and App Memory vs Free Memory is a good instant test, and the Swaps In and Out for sessions. If all your memory is wired and being used in Apps or you find lots of Swaps, time to upgrade the ram.
Swaps; Pages In/Pages Out relates to virtual memory used and is the process where files are written to disk in order to free up ram for processing immediate actions. So lots of swaps reflects how often your computer had to swap a file to run a process. With more ram, less swaps which are slower. This can be really compounded if your disk is full.
Open up Activity Monitor (in Utilities) Fire up whatever programs you normally use, do some editing and watch what happens. Also keep in mind that ram will be loaded/unloaded all the time depending on your activity.
Some programs will use lots more ram than others, and some are not great about releasing it. You might find out that by not having say PhotoShop and 10 other apps open, no problems.
Also, shutting down and restarting will free up your ram.
There are of course other things that can slow down a computer and invoke the SBB.