Zaplead
As an example a rule of thumb I use in a 206 is check what power (torque) it uses to maintain level flight at 80KIAS about 500' above your intended landing site. Add 20% (torque) to that figure to give you a IGE hover. To climb back out of the landing site add another 10% and if you have picked up some frieght or Pax add 1% for every 15Kg.
The advantage of this method is it automatically takes into account the altitude you are operating at.