Mouse
Small Mammals
The pocket-sized speedster that's cheap to keep but easy to underestimate!
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🤓 Did you know? A male mouse's strong smell comes down to one specific chemical, trimethylamine, that shows up heavily in his urine and barely at all in a female's or a rat's. It's why an all-male mouse cage needs cleaning far more often than the equivalent rat setup.
🗓️ The first week
The numbers a new owner needs in the first week, each from the article it links to. Rows with no link come from the encyclopedia.
- Bar spacing
- No more than about a quarter inch (6mm), and 5mm is sometimes recommended. Cages sold for small animals at three-eighths of an inch still let a determined mouse out.Setup guide →
- A wire cage, not a tank
- An aquarium cannot move air, so ammonia builds. Wire sides and top, a solid floor, and top mesh no larger than about 1cm square.Setup guide →
- Enclosure size
- At least 18 by 18 by 10 inches for 2 to 3 mice, with more floor and real climbing room on shelves and levels always the safer default.Setup guide →
- Bedding
- Dust-free paper, about 2 to 4cm deep, far shallower than a hamster's. No cedar, no aromatic pine, no cotton-wool nesting products.Setup guide →
- Nesting material
- A mouse in a room you find comfortable is below its own comfort range. The research puts the useful amount at six to ten grams, more than most pet cages hold.Enrichment guide →
- Wheel
- Solid, axle-free, 6 to 8 inches rather than a hamster's 10 to 12, and not the only enrichment.Setup guide →
- Temperature and humidity
- 64 to 79°F and 30 to 70% humidity. Damp, drafts, dust, and poor ventilation all raise respiratory risk.Health guide →
- Diet
- A pellet formulated for mice or rats at 20 to 25% protein, higher than the 14 to 16% a hamster or gerbil needs, which is why the hamster-and-gerbil tub is wrong.Feeding guide →
- How to feed it
- A measured ration once daily, some of it scattered for foraging. Pea-sized pieces of greens, carrot, pepper, or broccoli daily, pulled before they spoil. Eating its own droppings is normal, not illness.Feeding guide →
- Foods to avoid
- Grapes and raisins, rhubarb, citrus, chocolate, caffeine, and alcohol are toxic. Garlic, onion, raw beans, and raw potato out, and lettuce reliably causes diarrhea.Feeding guide →
- Females in groups, males usually alone
- Females need same-sex company, and it is not a close call. Adult males frequently fight seriously, so solitary housing is the common answer, which is a reason to think before choosing males.Enrichment guide →
- Picking one up
- Cup both hands and let it walk on; never scruff or lift by the tail tip. They jump roughly 13 inches straight up and 2 feet along, so handle low over something soft.Handling guide →
- Cleaning
- Spot-clean soiled corners often and leave some familiar bedding at a full clean. Stripping the cage makes a male re-mark it harder.Health guide →
- Adult size
- 2 to 3 inches (5 to 8 cm) body, plus a 3 to 4 inch tail, at 1 to 1.6 oz.
- Budget
- $5 to $20 each, and you are buying two or three. A first setup runs roughly $100 to $210, then $10 to $20 a month. A routine exam at an exotics practice is $35 to $75, and not every vet sees mice.Cost guide →
- Lifespan
- 1.5 to 2 years, the shortest commitment of almost any small mammal.Cost guide →
🚨 Emergency card
Call the vet now if you see any of these.
- Any breathing change: sneezing, nasal or eye discharge, labored or noisy breathing, an audible chattering
- Sudden weight loss
Book a vet visit promptly for these.
- A new lump anywhere on the body
- Dropped food and drooling
Mice decline quickly once a respiratory infection takes hold, and the organism behind most of it sits asymptomatic for a long stretch before flaring. Confirm ahead of time that a practice sees mice.
📰 Where to go next
How Much Does a Pet Mouse Really Cost?
$5 to $20 a mouse and you are buying two or three, $100 to $210 for the cage around them, and $10 to $20 a month after.
Mouse Enclosure Setup: Why a Wire Cage Beats a Glass Tank Here
Why the glass tank that suits a gerbil is wrong here, the quarter-inch bar spacing that keeps a mouse inside, and bedding shallower than you would guess.
What Do Pet Mice Eat? Diet, Portions, and Foods to Avoid
Why a hamster pellet is the wrong tub, portions sized to an ounce-and-a-half animal, and the reason eating droppings is a good sign.
How to Handle a Pet Mouse (Faster, Jumpier, and Easy to Underestimate)
The cupped-hand pickup, never the tail tip, and why 13 inches of vertical jump changes where you sit down to do it.
Common Pet Mouse Health Issues (Respiratory Disease Moves Fast)
Respiratory disease as the one to watch, mammary tumors, and why stripping the cage makes the smell worse.
Mouse Enrichment: Give Them Far More Nesting Material Than You Think
Six to ten grams of nesting material, the number behind it, and why a mouse in a comfortable room is cold.
🛒 What to buy
Prices and the reasoning behind each item are in How Much Does a Pet Mouse Really Cost?.
❓ Frequently Asked Questions
How tight does the bar spacing need to be for a mouse cage?
No more than about a quarter inch (6mm), and tighter still, down to 5mm, is sometimes recommended. That's tighter than most small pet cages, and mice can squeeze through gaps that would safely contain a hamster.
Is a glass tank a good enclosure for a pet mouse?
No, and this is a real difference from gerbil housing. A glass tank can't move enough air, so ammonia builds up inside it. A well-ventilated wire cage is the better choice for mice specifically.
How much protein do mice need?
More than a hamster or gerbil. General maintenance crude protein for a mouse runs 20 to 25%, with breeding or growing mice needing even more depending on strain, well above the 14 to 16% that's adequate for a gerbil.
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📰 Deep Dive
🐭 How Much Does a Pet Mouse Really Cost?
🐭 How to Handle a Pet Mouse (Faster, Jumpier, and Easy to Underestimate)
🐭 Common Pet Mouse Health Issues (Respiratory Disease Moves Fast)
🐭 Mouse Enclosure Setup: Why a Wire Cage Beats a Glass Tank Here
🐭 What Do Pet Mice Eat? Diet, Portions, and Foods to Avoid
🐭 Mouse Enrichment: Give Them Far More Nesting Material Than You Think
🩺 Health and More
🤩 Fun Facts
🐭 Eating Poop for the B12
Coprophagy in mice isn't just a fixed habit, it tracks real nutrient need. Researchers found mice fed a standard diet ate their own droppings about 9.6 times a day on average, but once the diet was fortified with vitamin B12, that dropped to roughly 4.7 times a day, direct evidence the behavior responds to actual nutritional demand rather than instinct alone.