There is a huge difference between going to the grocery, and hiking day after day over rough terrain. I'm sure you weren't suggesting someone try to thru hike with their dog carrying 50% of their bodyweight, but I just wanted to clarify. From what I understand, it is 10-20%. Ed never carries more than 5 lbs (he weighs 73 lbs), but that is just because I don't want weight on him.