Four to a Flush, post-flop, push all-in

[Tom22]

I have seen a lot of plays where someone would have the nut flush draw post-flop and push all-in. I understand the reason is that you have fold equity and also if someone calls you can still win when your suit hits. But mathematically, when would it be correct to make this move?

For example, if there is T100 in the pot. How many chips do you need behind and/or how many chips does your opponent need to have and/or what the fold equity percentage need to be to make this the correct play? I have seen this move many times on tv and would like to incorporate it in my game. Thanks in advance for the help.