Stolen from another thread:
You're touching on two things here - hops vs pellets (as your title suggests), and wet vs dry. I think the pellet-to-cone factor is +10%(weight) - as in when using cones, use 10% more. Additionally, if you were to use wet hops versus dry, tack on another 75-80%, as dried homegrown hops are 20-25% of their wet-weight.