Your question is a bit broad. Speed, rider and bike weight, grade, wind and effort by the rider are all factors. As an example, I ride an upgraded Class 1 Yamaha Cross Core with 250W output and a 500WH battery. My area is hilly with some grades over 20% and I ride a combination of paved and gravel. I generally average 16 to 18 mph. The Cross Core has four assist levels, (eco+, eco, standard and high). I typically ride in eco and I can ride about 65 miles and still have about 10% remaining. If I ride eco+, I can ride about 110 miles with 10% left in the tank.
I don’t know if this helps or adds to the confusion. It all comes down to the efficiency and capability of the bike and the amount of rider effort applied.