A flush draw has a roughly 20% chance of completing on the turn; therefore, you need to make them bet MORE THAN 20% of what's already in the pot.

Fortunately, there is an easy way of doing this: if you make a bet that's HALF the current pot size or higher, they are getting bad odds to draw (it's not exact, but it is a handy rule of thumb). The bigger a bet you make, the worse their odds are.
Hi, clarify for me please.
When ever I try to knock an opponent off a flush draw I always make the flop bet more that the pot total because the odds for the draw (flush ) are 2:1. I read this on one of the recent posts - pot odds/implied odds.

Dealing with 5:1 odds for the flush draw is taking one card at a time. I thought it was best to deal with your opponents draws as both cards to come. Same when I'm on the drawing hand.

cheers.