“The capybara is the largest living rodent at about 77 to 146 pounds, followed by the beaver and large porcupines. At the other extreme, pygmy jerboas and African pygmy mice weigh only a few grams, less than a U.S. quarter.”
Rodents are the largest group of mammals on Earth, with more than 2,000 species. They include animals so small they could sit on a coin and one so large it can outweigh an adult human. Seeing them side by side is the best way to appreciate just how varied this family is.
Rodent Size Comparison Chart
Weights and lengths below are typical adult ranges. Individual animals vary with sex, age, region, and diet. Body length excludes the tail unless noted.
| Rodent | Typical Weight | Body Length | Everyday Comparison |
|---|---|---|---|
| Capybara | 77–146 lb (35–66 kg) | 42–53 in (106–134 cm) | A large dog, like a Labrador |
| North American beaver | 24–70 lb (11–32 kg) | 29–35 in plus flat tail | A medium dog |
| Crested porcupine | 29–60 lb (13–27 kg) | 24–33 in | A beagle covered in quills |
| Patagonian mara | 18–35 lb (8–16 kg) | 27–30 in | A long-legged small dog |
| Lowland paca | 13–26 lb (6–12 kg) | 24–31 in | A spotted, stocky cat-sized rodent |
| North American porcupine | 11–30 lb (5–14 kg) | 24–35 in | A large house cat |
| Nutria | 9–20 lb (4–9 kg) | 17–25 in plus round tail | A big house cat |
| Groundhog | 4–13 lb (2–6 kg) | 16–20 in | A small cat |
| Muskrat | 1.5–4 lb (0.7–1.8 kg) | 10–14 in plus tail | A guinea pig with a long tail |
| Black-tailed prairie dog | 1.5–3.3 lb (0.7–1.5 kg) | 12–16 in | A loaf of bread |
| Guinea pig | 1.5–2.6 lb (0.7–1.2 kg) | 8–10 in | A loaf of bread |
| Fox squirrel | 1.1–2.2 lb (0.5–1 kg) | 10–15 in plus bushy tail | A pineapple |
| Chinchilla | 0.9–1.8 lb (0.4–0.8 kg) | 9–15 in | A grapefruit |
| Eastern gray squirrel | 0.9–1.3 lb (0.4–0.6 kg) | 9–12 in plus tail | A soda can with a tail |
| Fancy (brown) rat | 0.5–1.1 lb (250–500 g) | 8–10 in plus tail | A smartphone |
| Syrian hamster | 3.5–6 oz (100–175 g) | 5–7 in | A baseball |
| Gerbil | 2–4 oz (50–100 g) | 4–5 in plus tail | A large egg |
| House mouse | 0.5–1 oz (12–30 g) | 3–4 in plus tail | A few quarters |
| Roborovski hamster | 0.7–0.9 oz (20–25 g) | about 2 in | A golf ball, weighing less than a letter |
| Pygmy jerboa | a few grams | under 2 in plus long tail | Less than a U.S. quarter |
The Giants
Capybara: The Undisputed Champion
The capybara is by far the largest living rodent, heavier than the next-largest species by a wide margin. Its size is tied to its lifestyle as a grazing, semi-aquatic herbivore in South American wetlands, where a big body helps it process large amounts of fibrous grass and hold its own against predators. For more detail, see our full capybara size guide.
Beaver: The Engineer
Beavers are the second-largest rodents. The North American beaver and the Eurasian beaver are similar in size, and a big adult can reach 60 pounds or more. Their flat, paddle-shaped tail and dam-building habits make them unmistakable. Our capybara vs beaver comparison puts the two giants head to head.
Porcupines: Big and Prickly
Old World crested porcupines from Africa and southern Europe are among the heaviest rodents, sometimes rivaling beavers. North American porcupines are smaller but still substantial, and they are skilled tree climbers.
The Middleweights
Between the giants and the pocket-sized pets sits a wide band of medium rodents. Nutria, originally from South America, are semi-aquatic like capybaras and have become invasive in parts of the U.S. See our capybara vs nutria comparison. Groundhogs and marmots are burly burrowers that hibernate through winter, covered in our capybara vs groundhog and capybara vs marmot guides. Prairie dogs, muskrats, and pacas fill out the middle of the chart.
The Pet-Sized Rodents
Most pet rodents fall between about half a pound and two and a half pounds at the upper end, and just a few ounces at the lower end. Guinea pigs are the heavyweights of the pet world, followed by chinchillas and rats, then hamsters, gerbils, and mice. If you’re choosing a pet, size matters for handling, space, and lifespan. Our best pet rodents for beginners guide and guinea pig vs hamster vs rat comparison cover those trade-offs.
Capybara vs Guinea Pig
Capybaras and guinea pigs are close relatives in the cavy family, yet a capybara can weigh around 50 times as much. It’s one of the most striking size gaps between close cousins in the animal kingdom. Read more in our capybara vs guinea pig comparison.
The Tiniest Rodents
At the small end are jerboas, pygmy mice, and dwarf hamsters. Pygmy jerboas from the deserts of Central Asia weigh only a few grams and hop on long hind legs. The African pygmy mouse is similarly tiny. Among pets, the Roborovski dwarf hamster is the smallest common species, weighing less than an ounce.
Squirrels on the Scale
Squirrels show a lot of variation even within one family. Fox squirrels are the largest tree squirrels in North America, eastern gray squirrels are mid-sized, and American red squirrels are small and scrappy. Our guide to red vs gray vs fox squirrels explains how to tell them apart.
What About Extinct Giant Rodents?
Capybaras are big, but they’re small compared with some prehistoric relatives. Fossils from South America show rodents far larger than anything alive today. Josephoartigasia monesi, known from a skull found in Uruguay, is often cited as the largest rodent ever. Estimates of its weight vary widely depending on the method used, but many put it at several hundred kilograms or more, comparable to a bull.
Why Are Rodents So Different in Size?
Body size is tied to diet, habitat, and survival strategy. Small rodents can live in tiny spaces, reproduce quickly, and get by on seeds and insects. Large rodents like capybaras and beavers need more food, but their size helps them digest tough plant material, conserve heat or water, and deter predators. Semi-aquatic lifestyles in particular seem to favor bigger bodies.
Does Size Affect Lifespan?
Across rodents, bigger species tend to live longer. Mice and dwarf hamsters rarely live past two or three years, while guinea pigs often reach five to seven, and capybaras can live around a decade or more. Chinchillas are the notable exception. Despite weighing less than two pounds, they can live 15 years or longer, and naked mole-rats, which weigh about as much as a mouse, are famous for living more than 30 years in captivity. Size is a useful rule of thumb, but diet, metabolism, and lifestyle all play a role. See our capybara lifespan guide for how the largest rodent ages.
How Size Changes Care Needs for Pet Rodents
For pet owners, a rodent’s size shapes almost every care decision. Larger pets like guinea pigs and chinchillas need much more floor space and eat more hay, which raises monthly costs. Mid-sized rats need tall cages for climbing. Small hamsters and gerbils need less room overall but still need deep bedding and enough floor space to run and burrow. Tiny species such as Roborovski hamsters are quick and fragile, so they are better for watching than handling. And at the far end of the scale, a capybara needs a pool, a fenced yard, and a companion, which is why so few people can realistically care for one.
Frequently Asked Questions
What is the biggest rodent in the world?
The capybara is the biggest living rodent, weighing up to about 146 pounds.
What is the second-largest rodent?
The beaver is generally considered the second-largest rodent, with large adults weighing 60 pounds or more.
What is the smallest rodent?
Pygmy jerboas and African pygmy mice are among the smallest, weighing only a few grams.
Is a capybara bigger than a beaver?
Yes. An average capybara is heavier and taller than an average beaver.