What is the difference between mice and rats?

Well the size difference is the biggest clue that what you have are mice and not rats. Rats are MUCH larger than mice, proportionately their tails are longer and thicker and they weigh much more. Another way to tell is that a mouse's tail is always the same length or longer than their body, a rat's is always shorter and thick with a coarse scaly feeling to it, while a mouse's tail is generally soft and downy since it is furred. The feet of mice are small in proportion to their bodies, whereas a rat's are actually quite large. A rat's muzzle is quite broad as it gradually tapers from their head to the tip of their nose, a mouse's muzzle is quite pointy. Their waste is another way to tell. Mice feces is small and hardens quickly. It's generally about the size of half a piece of rice, whereas rat feces is long and quite large, obviously not hardening as fast. I have 2 pet mice, too, although wish I could have pet rats, but the province I live in has strict laws against keeping rats as pets.

Try this site: http://www.ratbehavior.org/RatsMice.htm :)