Range is a very wide and complicated target. My rule for estimating lately has been to figure about 1 mi/AH. Sure - flat road, mild motor/controller, pedaling hard, no wind, mellow load, most eBikes can get 4-6x that easy.
But, you don't want to underestimate things do you? It sucks to get stuck with no power on all but the most advanced ebikes. My very efficient Panasonic can do 10 miles on 2AH. My hot rod, 500W, throttle bike, riding like I stole it will be lucky to get 1 mile from 2AH. Neither is fun to pedal with a dead battery so estimating worst case is usually the best way to approach.
See the difficulty estimating eBike range? Nevermind the voodoo manufacturers use to arrive at their numbers.