Mouse vs Rat: How to Tell Them Apart and What to Do Next

What Is the Difference Between a Rat and a Mouse?

The difference between a rat and a mouse starts with size: an adult house mouse usually weighs 0.35 to 1.1 ounces (about 10 to 30 grams), while a Norway rat weighs about one pound (about 450 grams), according to the University of Arkansas Cooperative Extension. Mice and rats are different species (Mus musculus for the house mouse, Rattus norvegicus and Rattus rattus for the two common rats), so a mouse never grows into a rat. Use the features below together, not one at a time.

Body Size

Body size is the fastest clue. A house mouse measures about 5 to 7 inches (about 13 to 18 cm) from head to tail tip (UC IPM). A Norway rat measures about 11.5 to 18 inches (about 29 to 46 cm) in total, and a roof rat usually about 13 to 18 inches (about 33 to 46 cm). Health Canada notes that a rat can weigh up to 0.5 kilograms (1 pound). If the animal could sit comfortably in the palm of your hand, it is most likely a mouse or a very young rat.

Snout

Snout shape separates a mouse from a Norway rat. The house mouse usually has a slightly pointed nose. The Norway rat has a blunt snout, while the roof rat usually has a more pointed muzzle, so snout shape alone will not tell a mouse from a roof rat (UC IPM, University of Arkansas).

Ears

Ears usually look large on a mouse compared with its head (Health Canada). On a Norway rat, the ears are small: folded forward, they usually do not reach the eyes. On a roof rat, the ears are larger and usually reach the eyes when folded forward (UC IPM). Mice also tend to have small, black, slightly bulging eyes.

Tail

Tail shape and length are reliable on adults. A house mouse has a thin tail with almost no fur and visible scale rings. A Norway rat's tail is thick, scaly and hairless, darker on top and paler below, and shorter than its head and body. A roof rat's tail is longer than its head and body combined: pulled forward along the back, it reaches at least the snout (UC IPM). The old idea that rat tails are hairy is wrong.

Fur Colour

Fur colour helps less than size, because both animals are brownish or grey. The house mouse is light brown to dark grey with a lighter belly (Health Canada). The Norway rat is usually grey-brown on top and white to light grey underneath, though some are reddish or almost black (Government of Alberta). A white belly with white feet and a sharply two-toned tail points to a deer mouse, covered below.

How Do You Tell a Baby Rat From a Mouse?

A baby rat vs mouse comparison comes down to proportions: a young rat typically has a head and hind feet that look too big for its body, while an adult mouse is usually small but evenly proportioned (University of Arkansas, UC IPM). This is a common identification mistake, because a juvenile rat can be about the same overall size as an adult mouse.

Head Size

Head size gives a young rat away. A juvenile rat has a large, chunky head compared with its body, a bit like a puppy. An adult house mouse has a small, delicate head with a pointed nose and ears that look big for the head.

Hind Feet

Hind feet are the second check. A young rat has long, heavy back feet for its body size. A mouse's feet are small and dainty. If you have a photo, compare the length of the back foot with the length of the head: oversized feet mean rat.

Trap Size

Trap size is why the baby rat question matters. UC IPM notes that small juvenile rats often will not trigger a rat-sized snap trap, so you should identify the pest before you set traps. Rats usually reach maturity at about 3 months, so if you see young rats, adults are likely nearby.

How Do You Tell Mouse vs Rat Signs Apart?

Mouse vs rat signs differ mainly in scale: droppings, gnaw marks and holes are all bigger when rats are involved. Many people never see the animal, so these clues are often all you have. For a full list of warning signs, see our guide to the signs of mice.

Droppings

Droppings are the most useful sign. Mouse droppings are usually 1/8 to 1/4 inch (3 to 6 mm) long, rod-shaped and pointed at the ends (University of Arizona Cooperative Extension). Rat droppings can be as large as 3/4 inch (about 2 cm) long (University of Arkansas), and Norway rat droppings are typically blunt at both ends, shiny black and about the size of an olive pit, around 1.25 to 1.5 cm (Government of Alberta). Young rats leave smaller droppings, so look at the biggest ones you find. Our mouse poop vs rat poop guide compares them in detail.

Gnaw Marks

Gnaw marks show the size of the teeth. Mice usually leave fine, scratchy marks about 1/12 inch (2 mm) wide, while rat tooth marks are about 1/6 inch (4 mm) wide (UC IPM). Look on food packaging, baseboards, door edges and stored boxes.

Entry Holes

Entry holes are bigger for rats. Rat holes are usually 2 inches (about 5 cm) or larger, while mouse holes are often 1.5 inches (about 4 cm) or less (University of Arkansas). Norway rats also dig burrows in soil along foundations, with entrances usually about 5 to 7.5 cm (2 to 3 in) wide (Government of Alberta).

Rub Marks

Rub marks are usually dark, greasy smudges left by oil and dirt on the rodent's fur along walls, pipes and beams where it travels often (University of Arkansas). Both rodents leave them, and they show the routes worth trapping along.

Musty Odour

A musty odour is a strong sign of house mice. The University of Arkansas calls the characteristic musty smell a positive indication that house mice are present, especially in larger or long-standing infestations.

Nests

Nests often point to mice when they are small balls of shredded paper, fabric or insulation, usually about 4 to 6 inches (about 10 to 15 cm) across, tucked in drawers, wall voids, closets or attics (University of Arkansas). Norway rats usually nest in burrows outside or at ground level.

How Do Mice and Rats Behave Differently?

Mice and rats behave differently in ways that change how you control them: mice are curious and stay close to home, while rats are cautious and roam much farther.

Reaction to New Objects

Reaction to new objects is the biggest behaviour difference. House mice readily try new foods and investigate new things. Rats often quickly detect and avoid new objects in their territory, such as a trap or bait (University of Arkansas), and roof rats may avoid them for several days or weeks (UC IPM). This is why rat traps often need a warm-up period before they work.

Travel Range

Travel range is small for mice. A house mouse usually moves within an area of about 10 to 30 feet (about 3 to 9 metres) across and seldom goes farther for food. A Norway rat normally covers an area about 100 to 150 feet (about 30 to 45 metres) across (University of Arkansas). This is why mouse traps belong close to where you see activity or droppings.

Water Needs

Water needs differ too. House mice do not need to drink water to survive, because they get moisture from their food (UC IPM). Rats typically need about 1/2 to 1 ounce of water a day when eating dry food (University of Arkansas), so leaks, drains and pet water bowls matter more with rats.

Nesting Height

Nesting height depends on the species. Norway rats usually burrow and live mostly at ground level or in basements, and they are generally strong swimmers. Roof rats are agile climbers that usually prefer attics, upper floors and wall voids (UC IPM, University of Arkansas). Mice nest wherever it is warm and sheltered, from basements to attics.

Breeding Speed

Breeding speed is high in both. A female house mouse may have 5 to 10 litters a year of about 5 or 6 pups each (UC IPM). A female rat may average 4 to 6 litters a year, with about 6 to 12 young per litter (University of Arkansas). Mice usually live about 9 to 12 months, and wild rats on average less than one year.

Which Mice and Rats Live in Canada?

Canada's homes usually deal with two mice, the house mouse and the deer mouse, and two rats, the Norway rat and the roof rat. Where you live changes which ones you are likely to meet. For more mouse species, see our mice identification chart.

House Mouse

The house mouse is the mouse most often found inside Canadian homes. It is usually light brown to dark grey with a lighter belly and large ears (Health Canada), and its tail is nearly hairless. Like rats, it is not native to North America and likely arrived with ships from Europe and Asia.

Deer Mouse

The deer mouse is brown or grey with a white belly and white feet, and the white underside of its tail is the easiest way to recognise it (Health Canada). It also has larger eyes than the house mouse. This matters because Health Canada names the deer mouse as the most common carrier of hantavirus, so never sweep or vacuum its droppings.

Norway Rat

The Norway rat, also called the brown rat, sewer rat or wharf rat, lives in almost every inhabited region of Canada (The Canadian Encyclopedia). It is the stocky, blunt-nosed rat with a tail shorter than its body that digs burrows along foundations. Despite a common mix-up, it is not the "ship rat": that name generally belongs to the roof rat.

Roof Rat

The roof rat, also called the black rat or ship rat, is sleeker, with a pointed muzzle, large ears and a tail longer than its body. In Canada it was historically found mainly along the BC coast, and the BC government reports that rats are now found in parts of the province's interior as well.

Rats in Alberta

Rats in Alberta are rare because the province runs a Rat Control Program to keep its rat-free status; small infestations are occasionally found and dealt with. The Government of Alberta says many reported "rats" turn out to be muskrats, pocket gophers, ground squirrels, bushy-tailed wood rats or mice. If you think you saw one, take a photo, note the location and call 310-FARM (3276).

What Should You Do After Identifying a Mouse or a Rat?

After identifying a mouse or a rat, match your response to the species: the right trap size, the right gap size to seal and the right level of caution with poison baits.

Rat vs Mouse: Which Is Worse?

Rat vs mouse damage is usually worse with rats. Rats can burrow under foundations and slabs and gnaw electrical wiring and water pipes, while both rodents can damage insulation and contaminate food with hair, urine and droppings (University of Arkansas, the Government of British Columbia). Health Canada notes that both are carriers of disease, which can include salmonellosis and leptospirosis. Mice, though, can be harder to clear out of a home because they breed fast and need only a few crumbs. If you think you have both, read about mice and rats at the same time.

Traps

Traps work for both, as long as the size fits. Health Canada says snap traps and electronic traps are very effective when well placed and set properly, and advises checking all traps daily. For rats, allow a warm-up period of 3 to 4 days: bait the traps without setting them so the rats get used to them. Our guide on how to set a mouse trap covers placement and bait, and our picks for the best mouse trap compare models.

Sealing Entry Points

Sealing entry points is what keeps the problem from coming back. Health Canada says mice can squeeze through cracks as small as a dime, while rats can get through a quarter-sized hole. UC IPM recommends sealing any opening larger than 1/4 inch to help keep out both. Health Canada suggests steel wool around pipes before caulking, fine metal mesh over vents and metal weather stripping under doors. Our guide to finding mice entry points walks you through it.

Poison Baits

Poison baits need extra care, especially with children and pets. In Canada, rodenticides sold to homeowners must be used in bait stations (Health Canada), and the Government of British Columbia restricts the sale and use of the strongest second-generation anticoagulants (brodifacoum, bromadiolone and difethialone). Check the label for a PCP number, follow it exactly, and never use poison as your only method.

Safe Cleanup

Safe cleanup protects you from germs in droppings and urine. Health Canada advises against sweeping or vacuuming dry droppings, because the dust can make you sick. Wear rubber gloves and a dust mask, dampen droppings with a bleach and water solution, then wipe them up. See our step-by-step guide on how to clean mouse droppings.

When to Call a Pest Control Professional

Calling a pest control professional makes sense when you see rats, find burrows along your foundation, or keep catching mice after a few weeks of trapping. A licensed professional can confirm the species and find entry points, and Health Canada notes that commercial rodenticides must be applied by a certified professional. Our guide to mouse and rat pest control explains what to expect, and you can get a quote from a recommended local exterminator through Pest Agent's referral form. For more rodent guides, visit the mice hub.