From observation, I'd say that dogs tend to cover more miles on a hike than their owners do, due to their restlessly walking ahead, then returning, or else circling out away from the trail and then coming back to it. I attribute this to their desire to smell their surroundings, as their preferred method of sensory input. A dog may easily walk twice as far as its owner on a hike.

As for total miles per day, dogs, like their owners, vary in their conditioning, so you should experiment with your dog by working your way up to a level the dog seems to enjoy without wearing out or getting sore paws..

Another observation is that a human in really top condition can walk much further in a day than a dog can. This doesn't apply to humans in average condition (at least, average for the USA and other urbanized countries). So, if you are an athlete and plan to walk 20 miles a day, you should probably leave the dog home.