It is basic math. 9 cards of the remaining 47 cards complete the draw of the remaining 47 cards. Call it 19%. it really depends on the remaining stacks and the bet size.
Let's say you called 3BBs on the button with JTs. With 20 BBs left in both your stacks you check and the villain bets 1/2 pot. You need to call 3BBs to win 9BBs or 33%. If you call and hit you need to be sure the villain will call at least one more bet, otherwise you are losing money.
But say there are two villains and one bets and one calls. There are 15BBs in the pot and you only need to call 3BB more. You have the odds
, no matter what happens. It gets way better if you have a straight draw too (6 more outs) or 2 over cards (6 more outs).
If you are short, with say 6 more BBs, than you can push. The villain will usually call 3 more so you are betting 6BBs to win 12 BBs, but get to see 2 cards. The odds of hitting at now 9/47 + 9/46 or 38%. Not bad.
The thing to remember is the villain only has a hand 35% of the time and sometimes he will fold.