How this actually works
RAM sets your starting budget, then everything else spends it down. Operating system and browser choice both carry real, measurable overhead differences: Chrome is genuinely one of the heavier browsers on memory, Linux is genuinely lighter than the alternatives, and ChromeOS is genuinely built around the assumption that you won't be doing much beyond browsing. Extensions and background apps like Discord or Slack each take a real, ongoing slice, whether or not you're looking at them.
The number that matters most, though, is the one you type in yourself: how many tabs you already have open. That's not a modifier, it's a direct subtraction from your remaining budget. Enter it honestly and the rest of the calculator is really just doing arithmetic on a problem you already have.
Should you actually trust the result?
No. Real memory usage depends on what's actually running in each tab, not just the tab count, and this is a joke calculator on a website called Useless Calculators. If your fan is already screaming, close some tabs. You don't need a website to tell you that.