How Big are Mice? Size Comparison!

In case you didn’t know, mice are small. But don’t let their small figure fool you…they can cause a huge ruckus.

Their smallness is also not consistent. Just how small each one is depends on a variety of factors, including their age and species.

And while it may seem trivial, the size of a mouse is actually an important characteristic to familiarize yourself with, for it will help you distinguish them from rats. Use this article as your reference guide.

Stages of development for a mouse

When people talk about the size of mice, most are automatically referring to the size of house mice. House mice are by far the most common type of mice that people deal with as invasive pests or own as house pets. For this reason, this article is mostly concerned with the size of house mice.

Like all mammals, mice continue to grow until they reach adulthood. Once birthed, the become pinkies, then fuzzies, then weaned mice, then finally adults. A good tool for size comparison is a quarter (US currency) when dealing with baby and infant mice (a quarter is just under an inch in diameter).

Pinkies are between 1 and 5 days old and are between half an inch and one inch long. They can weigh anywhere from half a gram to three grams. A pinky is no larger than the size of a quarter (they are SMALL!).

After five days, pinkies become referred to as fuzzies for their new, small coat of fur. Mice are known as fuzzies from when they are 6 days to old to when they are 13 days old. They can measure anywhere from one inch to one and a half inches long and can weigh between three and six grams. Fuzzies can fit on about one and a half quarters.

After the fuzzies stage, their eyes open. You may also notice a thicker coat of fur, and incisor teeth showing. And by the time they are two weeks old, females will have nipples.

Before they are adults, mice are called weaned mice. Weaned mice are between three and four weeks old. They can be anywhere from two to two and a half inches long and can weigh between 13 to 18 grams. Weaned mice are about the size of two to two and a half quarters in length.

From 28 days old and on, a mouse’s head will be approximately the same length as a quarter, and after 35 days, mice become sexually mature. They also reach puberty at six to eight weeks of age. This is why a mouse is such a threat to homes. Because the early sexual maturity and fast gestation period, a female mouse can have between 5 and 10 litters per year (3-14 pups per litter). Rats are only marginally better. A female rat typically has six litters per year (5-10 pups per litter).

Mice adulthood is somewhat ambiguous. Some scientists and researchers say that mature adult mice range between three and six months, while others say that mice reach adulthood once they hit puberty between six and eight weeks of age. Generally speaking, house mice live up to a year.

Regardless, a full grown house mouse is anywhere from five and a half to seven inches in length, including the tail.

How big is a full grown mouse?

A full grown house mouse is anywhere from five and a half to seven inches long, including the tail.

An adult house mouse head and body length alone is between 2.5-3.5 inches and its tail length can be between 2.75-4 inches.

They weigh between 0.5-1 ounce.

Size of mice compared to rats

While rats and mice share many similarities and behavioral characteristics, rats are generally larger than house mice.

The Norway rat, also called the common rat, street rat, or sewer rat, is the type of rat most people encounter in their daily lives. This rat can measure up to 40cm (15.7 inches) in length, which is a great deal longer than that of a house mouse. Norway rats also weigh between 0.31 and 1.1 lbs (up to 16 times heavier than a house mouse).

Outside of cities and in more exotic locations, you may encounter other types of rats. The largest species of rat is called the Bosavi woolly rat, which was discovered in Papua New Guinea. They can grow up to 32.2 inches from nose to tail and weigh up to 3.3 pounds…about the size of a cat! On the other hand, one of the smallest types of rats is called the Osgood’s Vietnamese rat. They are about 5 to 7 inches long, which is about the size of a house mouse, but you likely won’t see this rat unless you are in Vietnam.

And like mice, a young rat will be much smaller than a full grown one. Although, you are unlikely to see a baby or young rat on its own without its mother in your home unless you have a full blown rat infestation (which you should have already noticed by now).

While numbers can be useful, I find that visual comparisons provide extra content to help illustrate the differences in size between rats and mice. A quick search on the internet on rat and mouse sizes will yield images that show you clear sizes of them.

And when in doubt, trust your instincts. If you see a rodent scurry across your kitchen floor and couldn’t estimate the length of it in inches, it’s okay to rely on your intuition. The most common rats (Norway rats) are noticeably larger than house mice. If you see a rat in your home, it will likely startle you or freak you out even more so than if you saw just a mouse.

How to tell if you have mice or rats?

There are numerous ways to tell if you mice or rats. The best way is size. If can comprehend their size differences, it’s quite easy to distinguish between the two rodents.

However, it’s possible that you haven’t yet actually seen a rodent, but rather have seen signs of a rodent’s presence. In this situations, it’s still possible to determine what kind of rodent you have, particularly if you have noticed any droppings.

Rat and mouse droppings look very different and can be closely observed if found in your home.

Rat droppings are usually shiny and black. Rat droppings are between a quarter and a half of an inch long. Rat droppings are also capsule shaped and have blunt ends to them.

Mouse droppings have more pointed ends. Their droppings are typically between a fifth to a quarter inch in length.

If you still are really unsure of your situation, it is always best to contact a pest control expert. A pest control expert can assess your specific situation and sometimes even provide an initial, free consultation.

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