That's the tough part. To do this, you need to first think about what his range is.

When you know his range (or have an estimate), you need to know how to count

*combinations* of hands.

Then, you need to decide which hands in his range he will fold to your bluff.

When you know this, you just divide

*combinations of hands he will fold* by

*total combinations of his range*.

For an easy example, if you decide he has 50 combos in his range and he will fold 25 of them, he will fold 50% of his range.

Now, for your bluff to be profitable you need to make sure that % of his range that he folds, is bigger than the amount needed for your bet to be profitable.

For example, if you bet a size that needs 33% fold equity to be profitable, he needs to fold

*more* than 33% of his range.

I hope that's clear enough. Estimating fold equity can be pretty hard