What I am trying to get at is that there is no hard and fast rule. There are just too many variables. Like Goby said your tank will tell you. I.E. too high a nitrates that will not decrease or require a lot of filtering, heavy skimming, refugium with macro algae, just to put a small dent in the numbers. Fish constantly fighting for space. One fish always kicking the bucket.
Your tank will always seek a balance with or without your help. If you overstock, eventually things will start dying until a balance is reached. The trick is to find the balance without pushing it to the limit.
Every tank is different, and it depends on what fish you have/plan to keep. A tank full of gobies will not stress the system as much as a tank full of a more aggressive messy eaters. A tank with a ton of LR/DSB/Heavy Skimming/Refugium/etc can handle a heavier load than a system that has just a mechanical filter. But if the power goes out for a few hours you could be toast.
I know that I am probably not helping you much, why don't you give a run down of what you have and what you want and a more educated answer can be presented.........