and how do I calculate it?

Thanks

EDIT Think I figured it out.
For lets say AKxxhh to hit a flush on the flop:

(11/48) x (10/47) x (9/46) = 1% and for AKxxds it's twice.

For AKxxhh to hit a flush draw:

1st card non-heart and 2nd and 3rd card a heart:

(39/48) x (11/47) x (10/46) = 4.134%

This chance is the same for 1st card heart, 2nd misses, 3rd card heart and if 1st and 2nd card is a heart and 3rd card non-heart, so chance for flopping a flush draw on the flop is around 12.4% for a single suited hand.

Calculating as above for AKxxds chance is 3 x (26/48) x (22/47) x (10/46) = 16.5% to flop a flush draw, but this doesn't seem reasonable if the chance for flopping a flush draw with a single suited hand is 12.4%.

Back to the original question: how do we calculate this?