Norway Rat Size: How Big Are These Unwanted Rodents?

Norway Rat Size

Are you curious about one of the largest rats in the world? Let’s dig deep into the realm of the Norway rat, also renowned as the brown rat or sewer rat and explore everything you need to know about this fascinating creature. In this piece of construct, we’re going to unfold the secrets behind the Norway rat size, behavior, habitat and more. So, if you’ve ever wondered just how big these rodents can get, you’re in the right place! Without further ado, let’s get started.

KingdomPhylumClassOrderFamilyGenusScientific Name
AnimaliaChordataMammaliaRodentiaMuridaeRattusRattus norvegicus
Taxonomic Classification of Beaver (Castor Canadensis)

Norway Rat Size

Norway rats might seem small scurrying through the shadows, but they’re, in reality, one of the biggest rodents pests you’re likely encounter. Let’s spotlight the Norway rat size.

An adult Norway rat can reach a whopping 16 inches (40 cm) from nose to tail tip. Their bodies alone measure around 9.5 inches (25 cm), which is about the length of a large smartphone. The average Norway rat weight is anywhere from 0.5 to over 1 pound (226 grams to 500 grams).

Notwithstanding the Norway rat size, they can squeeze through openings as small as half an inch (1.3 cm). That’s about the width of your pinky finger! Their powerful jaws and ever-growing incisors can exert up to 22,000 pounds per square inch of pressure. The size of this species can be directly correlated to food availability. In areas with abundant food scraps – like urban environments – Norway rats tend to be larger than their rural counterparts.

Scientific Name

The Norway rat – a common and widespread pest – carries the scientific name Rattus norvegicus. This bi-nominal system of nomenclature classifies the rat within the genus Rattus, grouping it with other close relatives like the roof rat. The Norway rat species designation, norvegicus, refers expressly to Norway, though the misconception is that the Norway rat originated there. In reality, these adaptable rodents likely came from Central Asia, but the name stuck due to their early association with European ships.

Origin and Evolution

Evolutionary History

The Norway rat belongs to the Muridae family, which encompasses various rodents like mice, voles and other rates. Their evolutionary journey can be traced back to Eurasia around 50 million years back in time. Around 2 million years ago, an ancestor of the Norway rat diverged from the lineage leading to the black rat (Rattus rattus). This split likely took place due to changing environments and ecological niches. During the Pleistocene epoch (Ice Age), Norway rats adapted to colder climates, resulting in physiological changes from thermoregulation.

Genetic Composition and Diversity

The Norway rat has 42 chromosomes, with a genome size of around 2.77 billion base pairs. Research indicates genetic differentiation between Norway rat populations in Europe and North America. The variation might be linked to founder effects and adaptations to local food sources and predators.

Environmental Adaptations

Norway rats are highly adaptable, thriving in diverse environments like sewers, farms buildings and even deserts. These resourceful rodents possess excellent spatial memory and can navigate intricate environments. Their keen sense of smell helps locate food and avoid predators.

Distribution and Population

Geographic Range

The Norway rat is a cosmopolitan species, that is, it inhabits most of the world. They’re found on every continent except Antarctica. Their established populations are found in Europe, Asia, North and South America. Albeit the “Norway” in their name, Norway rats originated in northern China and Mongolia around 50,000 years ago. They spread westward along trade routes, reaching Europe by the 18th century.

Population Dynamics

Though approximating Norway rat population is challenging, researchers suggest densities can range from 2-300 individuals per hectare in urban environments. Their populations tend to fluctuate built upon food availability, shelter and predator pressure.


Continents All except Antarctica
Bio-geographical RealmsBio-geographical Realms Palearctic; Introduced in Nearctic, Afrotropic, Indomalayan
Biome Urban environments, Forests, Grasslands, Wetlands
Climate ZonesTemperate, tropical, subtropical


Norway rat Habitat

The captivating Norway rat size may steal the spotlight, but its habitat holds equally fascinating secrets.

Habitat Preferences

Norway rats can thrive in both natural and man-made ecosystems. They feature a strong preference for environments providing shelter, food sources and water. Speaking of their specific microhabitats, they may crate elaborate burrow systems near water sources with multiple entrances and chambers. While both the Naked Mole-Rat and the Norway rat are rodents, the former is adapted to living in underground colonies, while the latter is often found in urban environments.

Habitat Utilization Patterns

Norway rats are chiefly nocturnal animals, that is, they’re most active at night when there’s less risk of encountering predators. Their populations may showcase some seasonal movements depending on food availability and weather conditions. In colder climates, they might move closer to buildings for warmth and access to food sources during winter.

5 Norway Rat Facts

  • Norway rat are phenomenal swimmers. They can tread water for up to three days and navigate underwater for 300 meters!
  • Being astonishingly agile, they can jump vertically up to a meter (3.3 ft) and scale surfaces with incredible ease.
  • These species are remarkably intelligent. They can learn complex maze layouts and even transmit this knowledge to their offspring.
  • Concerning the Norway rat size, they can reach a total length of 16 inches (40 cm) from nose to tail tip, with a body length of around 9.5 inches (25 cm).
  • A female Norway rat can reach sexual maturity in 5 weeks and produce a litter of up to 12 pups every 3-4 weeks.


Norway rat Appearance

Though the Norway rat size may command attention, its appearance harbors a wealth of enthralling secrets, waiting to be revealed.

Physical Characteristics

Size: Norway rats are one of the largest rodent species. Adults generally measure 16-20 inches (40-50 cm) in total length, including the tail, with body length of 7-9 inches (18-23 cm).

Shape: They’ve a robust, heavyset body with a blunt snout, small eyes and short, rounded ears that don’t fold over.

Color: The Norway rat’s fur is coarse and short, normally ranging in color from grayish-brown to reddish-brown with a lighter underside that can be grayish-white or yellowish.

Distinctive Feature: One of the most recognizable features of Norway rats is their tail. Unlike some other rodents, their tail is shorter than their body, hairless and scaly – appearing pink or brown in color.

Norway Rat Anatomy

Color(s) Brownish-gray, sometimes with scattered black hairs
TongueRough and spiny
ClawsSharp and curved
MouthSmall with sharp incisors
JawStrong for gnawing through tough materials
TeethContinuously growing incisors
NosePink and well-developed
FeetFive toes on each foot with rough pads
Skeleton Bony skeleton with a flexible spine

Reproduction and Life Cycles

Reproduction and Life Cycles

Even as the Norway rat size captures our fascination, its reproduction and life cycles are brimming with equally intriguing tales yet to be told.

Mating System

Norway rat’s mating system is defined as promiscuous – where both males and females mate with multiple partners throughout their breeding season. They don’t exhibit monogamy or form long-term pair bonds.

Reproductive Biology

In conjunction with the Norway rat reproduction, they can breed year-round, specifically in areas with stable temperatures and abundant food resources. Nonetheless, breeding activity may be more pronounced during spring and fall. Females nurse their young for 3 to 4 weeks, offering milk and grooming them. Females can reproduce very quickly. Following a gestation period of around 21-23 days, they can give birth to large litters – 5-12 pups per litter.

Life Cycle Stages

Norway rat pups are born blind and hairless. Their fur grows in within a week and their eyes open around 14 days old. By 3-4 weeks, they are weaned and become independent. Sexual maturity is reached at around 3-4 months of age. The Norway rat’s lifespan, in the wild, is relatively short, typically lasting only 1-2 years. In controlled laboratory settings, they can live up to 3-4 years.

Mating Habits

Mating BehaviorPromiscuous – females mate with multiple males
Reproduction SeasonBreeds year-round, but more frequent in warmer months
Litter Size5-10 pups per litter
Gestation Period21-24 days
Independent Age3-4 weeks old

Diet and Lifestyle

Norway rat Diet and Lifestyle

While the Norway rat size captures headlines, its diet and lifestyle hold a trove of captivating narratives waiting to be explored.

Feeding Ecology

With respect to the Norway rat’s diet, they’re opportunistic feeders, typified as omnivores. Their diet comprises seeds, grains, fruits, vegetables, insects, eggs, small mammals, carrion and garbage.

Foraging Strategies

The keen sense of smell of Norway rats makes them excellent foragers. They can travel long distances at night, unpacking new areas and memorizing routes to reliable food sources. For further insight into the biology, behavior, and control of the Norway rat, we recommend visiting the website of the Centers for Disease Control and Prevention (CDC).

Threats and Conservation

Norway rat Conservation status

The Norway rat is not a species of conservation concern. In fact, the International Union for the Conservation of Nature (IUCN) Red List classifies them as “Least Concern.” Their population doesn’t face many significant threats in the wild. Nevertheless, there’re a few factors that can keep their population in check, including predators, habitat loss, disease and control measures.

Relationship with Humans

Cultural Significance and Symbolism

In mythology, Norway rats are linked with negativity. In Egyptian mythology, they were seen as harbinger of disease and death. Similarly, some Native American legends depict them as tricksters or symbols of chaos. In folklore, seeing rate in some cultures is regarded a bad omen, foretelling misfortune or illness. In contrast, in some parts of Europe, white rats were thought to bring good luck.

Diseases Carried by Norway Rats

  • Bubonic plague
  • Bubonic plague disease
  • Murine typhus
  • Hantavirus pulmonary syndrome
  • Leptospirosis
  • Rat-bite fever
  • Salmonella
  • Trichinosis

Media and Entertainment

In the realm of media and entertainment, these species have made their conspicuous presence in multiple genres:

  • Animal Farm (1945)
  • The Wind in the Willows (1908)
  • Dracula (1931)
  • Ratatouille (2007)

Norway Rat vs Roof Rat

Norway Rat vs Roof Rat

These comparative percentages are ballpark figures for a quick rundown and aren’t scientifically precise. Actual differences can fluctuate thanks to variables like species, environment and individual variations.

The Takeaways

Forge a path through an intriguing journey as we unfold fascinating facts about Norway rats – truly captivating animals that start with N. Join us in shedding light on their remarkable rundown!

Common NameNorway Rat
Other Name(s)Brown rat, common rat, sewer rat, wharf rat
Number of Species 1 (Rattus norvegicus)
Population SizeExtremely high (billions worldwide)
Lifespan 1-2 years (wild), up to 4 years (captivity)
Weight 11 oz – 1.25 lbs (312 g – 567 g)
Length Up to 16 inches (40 cm) (total)
Top Speed 5 mph (8 kph)
PredatorsSnakes, owls, foxes, cats
PreyInsects, eggs, small animals, fruits, vegetables, garbage
Most Distinctive FeatureLong, scaly tail, sharp incisors


Both the brown or Norway rat (Rattus norvegicus) and the black rat (Rattus rattus) are carriers of the Seoul hantavirus. While other animals can also carry the Seoul hantavirus, they are unable to transmit it to humans.

Both the brown or Norway rat (Rattus norvegicus) and the black rat (Rattus rattus) should be deemed hazardous due to their capability to carry and transmit diseases and parasites, both directly and indirectly.

Norway rats are thought to originate from the plains of Asia, specifically northern China and Mongolia.

You can take a plenty of measures, including sealing entry points, keeping food stored in airtight containers or setting snap traps or bait stations with appropriate bait.

Norway rats are known to consume a wide variety of food types, exhibiting an omnivorous diet.

Mudassar Ahmad

He is a seasoned blogger since 2012 and an M.Phil graduate in English Linguistics. He captivates readers with his eloquent prose and insightful perspectives. His passion for language and dedication to crafting compelling content make him a trusted voice in the online sphere. Explore the world through Ahmad's literary lens.

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