Is It a Norway Rat or a Roof Rat?
By the Clark Pest Entomology Team
Last updated: October 28, 2026
Quick answer: Start with weight and nest height. A Norway rat weighs 7 to 18 ounces, has a blunt muzzle and small ears and nests low. A roof rat weighs 5 to 10 ounces, has a pointed muzzle and a tail longer than its body, and nests above ground.
Which Rat Do You Have?
Clark covers two house rats in California and Northwestern Nevada. Tap the one that sounds closest to what you saw.
Norway Rat
Also called the brown, sewer or wharf rat. Clark's guide puts it at about 16 inches with the tail, with a stocky build and a blunt muzzle. It burrows and nests low.
Roof Rat
Sleeker, with large ears and eyes and a pointed muzzle. Clark's guide puts it at about 14 inches, and the tail makes up 8 of them. It climbs and nests high.
Norway Rat or Roof Rat? Side-by-Side Clues
UC IPM says young rats can be mistaken for mice, so check two or three clues together. If the animal is closer to mouse size, our house mouse guide may fit better.
| Clue | Norway rat | Roof rat |
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| Other names | Brown rat, sewer rat, wharf rat | Also called black rat, ship rat or Alexandrine rat |
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| Weight | 7 to 18 ounces | 5 to 10 ounces |
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| Build | Large and stocky | Sleek and agile |
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| Tail | Pulled forward over the back, it reaches the middle of the skull | Longer than the head and body combined |
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| Muzzle and ears | Blunt muzzle. Folded ears do not reach the eyes | Pointed muzzle. Folded ears reach the eyes |
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| Color | Brown with scattered black hairs. Clark's guide describes the belly as gray to yellowish white | Clark's guide says the black type is sooty black above and gray below and the Alexandrine type is brown-gray above with a yellowish-white underside |
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| Nests outside | Burrows along foundations, under rubbish and woodpiles | Shrubs, trees and dense plants such as ivy |
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| Lives inside | Basements and ground floors | Attics, wall voids and ceiling voids |
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| Travels from the nest | 100 to 500 feet a night | Up to 300 feet or more for food |
|---|
Clues Left Behind
Rub marks and gnaw marks
Rats leave smudges where their fur rubs against walls, pipes, beams and rafters. Their teeth leave marks about 1/6 inch wide, twice the width of a mouse's. Droppings near pet food or a food storage area are another sign.
Shapes on wires and fences at dusk
Roof rats are often seen at night running along overhead utility lines or fence tops. Noise in the attic or above a drop ceiling is another sign of rats. Roof rats climb well, so ask what is up high before you check the floor.
Holes under cans and compost
Norway rats dig. UC IPM lists burrows under garbage cans, compost piles and garden plants as a sign of rats, and says Norway burrows run along foundations and under rubbish or woodpiles.
What Rats Can Do to a House
Rats can carry disease. According to UC IPM, the most common illnesses linked to rats are typhus, leptospirosis, rat bite fever and foodborne illness such as salmonella. Rats that live around people do not carry rabies.
Plague is a different story. According to UC IPM, it is very rarely found in rats that live around people. It occurs in California in wild ground squirrels, chipmunks and sometimes woodrats. The CDC says plague occurs naturally in parts of the western United States and that people usually catch it from the bite of an infected rodent flea.
Damage can be just as serious. According to UC IPM, rats gnaw electrical wires, and roof rats in an attic create fire and electrical hazards. Rats may chew natural gas lines too. Bring in a professional if you hear scratching overhead.
Seal, Trap and Skip the Poison
Close the gaps, high and low
UC IPM says to seal every hole larger than 1/4 inch. The Nevada Department of Agriculture says a rat can pass through any opening wider than 1/2 inch, and UC IPM adds that young rats can squeeze under a door with a 1/2-inch gap. Plug gaps with sheet metal or wire screen. Rats chew through plastic, foam, wood and caulk. Because roof rats climb, check gaps above ground too.
Match the trap spot to the rat
UC IPM calls snap traps the safest and most effective way to trap rats. For Norway rats, set them close to walls, behind objects and in dark corners. For roof rats, UC IPM says traps may be needed both on the ground and up high, on ledges, shelves, branches, fences or pipes. Place them about 10 to 20 feet apart and keep them away from children and pets.
Why poison can backfire
Clark's guides note that a rat that eats bait can die inside a wall. The smell and the decay can draw insect larvae. Traps let you find and remove what you catch.
Clark's Expert Insight
Look up before you look down. Smudges on rafters, noise overhead and a rat on a fence top say roof rat, and that changes where the traps go. Set them only on the floor and a roof rat can walk right past.
Rat Questions Homeowners Ask
Is a wharf rat or sewer rat the same as a Norway rat?
Yes. Clark's guide lists brown, sewer, Hanover and wharf rat as other names for the Norway rat. It describes an animal about 16 inches long with a 7-inch tail. UC IPM puts the weight at 7 to 18 ounces.
How big is a roof rat?
Clark's guide gives about 14 inches, with a 6-inch body and an 8-inch tail. UC IPM puts the weight at 5 to 10 ounces and says the tail is longer than the head and body combined.
What color are roof rats?
It depends on the type. Clark's guide says the black rat is sooty black above and gray below. The Alexandrine rat is brown-gray above with a yellowish-white underside.
How long do rats live?
Clark's guides give about one year for both the Norway rat and the roof rat. According to UC IPM, Norway rats have 4 to 6 litters a year. Roof rats average 3 to 5 litters, with up to 8 young in each.
Are roof rats nocturnal?
According to UC IPM, rats are mostly active at night. Roof rats are often seen at dusk and after dark, running along overhead utility lines or fence tops.
Do roof rats carry disease?
They can. UC IPM lists typhus, leptospirosis, rat bite fever and foodborne illness. It says plague is very rarely found in rats that live around people.
When should I call a professional?
Call when you hear rats in the attic or walls, when traps keep catching them or when you cannot find the entry point. A technician can name the rat, trace how it gets in and build a plan for your property.