Rats and mice are in the same rodent family, along with moles, squirrels and hamsters, but they are quite different. Common types of rats in the U.S. are the Norway and roof rat, while house mice are commonly seen indoors. It's helpful to compare their differences so you know what you are dealing with in case of a rodent home invasion.
Look for size differences. A full-grown mouse may weigh a few ounces, while an adult rat may weigh as much as a pound. A young rat, while still hairless, is already the size of a full-grown mouse, and a baby or young mouse is very tiny.
Examine the rodent for larger ears and feet, which indicate a rat, or small, sharply triangular heads, which indicate a mouse. Rats also have thicker tails and smaller ears proportionately to their bodies.
Measure the length of their outdoor burrow to nest, which can be 3 feet or longer for a rat. A mouse will generally not go any deeper than 6 inches to a foot if they dig at all; they would prefer to live in a wall, or behind or under an appliance.
Observe signs of aggressiveness. If you corner a rat, it may jump up and attack to get away. A mouse tends to freeze or back off in absolute fear.
Examine dropping size. Mouse droppings range in length from 1/8 to 1/4 inch, whereas rats droppings are double that size, around 1/2 inch.
Look for oily stains, called run marks, rubbing off the sides of rats' bodies that will appear over time along a wall or opening. Mice also follow the same route of travel, being creatures of habit, with less evidence of their route.