A. At first glance, a young rat could be mistaken for an adult mouse. They are, after all, both closely related rodents but there are visible differences between the black or Norway rat (our most common rat) and the house mouse, regardless of their size. If you could get the two sitting quietly side by side for comparison, here is what you would look for:

Size – The typical body length (head plus torso) of an adult black rat averages 9 inches, not including the tail length of about 8 inches. The body length of an adult mouse averages about 3 inches (plus a 3 to 4 inch tail). A rat’s body in general is bulkier while a mouse’s body is more slender.

 

Tail – A mouse’s tail is about the same length as its head and body combined while the tail of a rat is shorter than its head and body combined. A black rat’s tail is dark above and pale beneath while a house mouse’s tail is uniformly dark.

Head – A mouse has a small head that is proportional in size to its body while a young rat has a large head for its body. A mouse has a more pointed muzzle while a rat’s nose is more blunt.

Ears – A mouse has large ears for its head size (you could pull them over its eyes) while a rat has proportionally small ears with hairs inside (if you get close enough to check!).

Feet – A mouse has small feet that are in proportion to its body, while a young rat has feet that are large compared to the rest of its body (sort of like a puppy!)