Pet mouse temperature guide: too hot, too cold and just right

What is the body temperature of a mouse?

A pet mouse's normal body temperature is 36 to 38°C (98 to 101°F), according to the MSD Veterinary Manual. That is close to ours, but everything else about a mouse runs faster: its heart beats 450 to 600 times a minute and an adult weighs only 20 to 40 g (about 1 oz).

That tiny size is the whole problem. A small body has a lot of skin for its weight, so it gains and loses heat quickly. The MSD manual says mice have a limited ability to control their body temperature and are very sensitive to both heat and cold. To cope, they widen or narrow the blood vessels in their tails to let heat out or keep it in. That is why the room matters so much more than it would for a cat or a dog.

What temperature should a pet mouse room be?

Aim for 18 to 22°C (64 to 72°F). Sources give slightly different ranges, so here they are side by side.

We follow the PDSA's 18 to 22°C as the target and the MSD manual's 26°C (79°F) as the line you should not cross. RSPCA Australia's 30°C top is written for a hotter country and sits right where the MSD manual says heatstroke starts, so we would not plan around it.

Humidity matters too. The MSD manual gives 30 to 70%. Air that is too dry, too warm or draughty can cause ringtail in young mice, where a tight ring forms around the tail and can cut off the blood supply. The RSPCA says to keep mice out of bathrooms and air-conditioned rooms for the same reason.

Where should you put a mouse cage?

In a quiet, lived-in room that stays steady all year. A spare bedroom or a quiet corner of a living room usually works. Use this list to check the spot before the cage goes in, and see our mouse cage setup guide for what goes inside.

• Out of direct sunlight all day, including late afternoon sun through a window
• Away from radiators, fires, cookers and the top of the fridge
• Away from draughts from doors, windows and air vents
• Not in a conservatory, garage, shed or greenhouse
• Not in a bathroom or a room with air conditioning blowing
• Away from loud noise, the TV and other pets
• A room thermometer at cage height

How do you know if a mouse is too hot?

An overheated mouse goes flat and slow. The PDSA lists these signs of heatstroke in small pets:

• Lying stretched out or flat on its belly
• Short, quick breaths
• Drooling or a wet chin
• Very sleepy, floppy or slow to react
• Eating less or not at all
• Fitting or falling unconscious

The RSPCA adds very hot limbs, ears or nose, and very dark red skin on them, to its list of signs a mouse needs a vet. A mouse that is only warm will move to the coolest corner, spread out and be less active. Treat that as a warning to cool the room now, before it turns into heatstroke.

What to do if your mouse has heatstroke

Cool it gently and ring a vet straight away. Heatstroke can kill, and the PDSA says to contact your vet immediately if you suspect it.

1. Move it somewhere cool. Take the mouse, or the whole cage, to the coolest shaded room in the house, as the RSPCA advises.
2. Use a cool, damp towel. The RSPCA says to wrap the animal in a cool, damp towel. Use cool water, not ice-cold.
3. Do not bathe it. The PDSA warns against putting small pets in water, because the sudden change in temperature can chill them.
4. Ring your vet. Phone while you cool the mouse, and say it is a suspected heatstroke so they see you quickly.
5. Travel cool. Carry it in a small carrier with a damp towel over part of it. The RSPCA suggests a quiet, air-conditioned car for vet trips.

How to keep pet mice cool in summer

Keep the sun off, keep the air moving and give them cool spots to lie against. These steps come from the PDSA and RSPCA summer advice.

1. Shade the room. Close the curtains on the sunny side of the house during the day, as the PDSA suggests.
2. Move the air. Open a window or run a fan in the room, pointed away from the cage so it never sits in a draught.
3. Use a frozen bottle. Fill a plastic bottle three-quarters full, freeze it overnight, wrap it in a towel and stand it outside the cage, against the bars. Both charities say outside: inside, it can leak or chill them.
4. Add cool surfaces. The PDSA suggests ceramic tiles or china cups. Check for sharp edges and make sure nothing can fall and trap a mouse.
5. Swap plastic houses for cardboard. The PDSA says plastic houses, dens and tunnels get warm and humid; a cardboard box with several exits stays cooler. Our guide to mouse hides and houses covers both.
6. Check the water twice a day. They drink more in heat. The RSPCA says check bottles morning and evening for blocked nozzles.
7. Offer a chilled treat. The PDSA suggests a small piece of apple, cucumber or celery from the fridge. See can mice eat cucumber for how much.

A crowded cage heats up faster. The MSD manual says overcrowding raises the risk of heatstroke, so in a heatwave a large cage is safer than a small one. Our mouse cage size guide gives sizes by group.

How to keep pet mice warm in winter

Keep the room above 18°C (64°F), and give them more to nest in. Mice build their own nests and, with the right material, they keep themselves warm. Burgess and the RSPCA give the main points.

• Extra paper bedding for burrowing on cold days (see our mouse bedding guide)
• Plenty of nest material: plain paper, tissue or hay, never cotton wool or fluffy bedding, which the RSPCA says can tangle round legs
• Bedding kept dry; Burgess warns damp bedding in cold weather can make small pets ill
• A cage moved away from windows and outside doors
• A slightly bigger food portion if they seem hungrier; Burgess says small pets may need a little more in winter
• No aromatherapy oils, wood-burning stoves or non-stick pan fumes near the cage, which Burgess lists as hazards

A mouse kept with others is better placed in winter than one alone, because a group can share a nest. That is our reasoning, not a figure from a source, but the RSPCA already says mice should not live alone. See male or female mice for building a group.

How do you know if a mouse is too cold?

A cold mouse sits hunched, fluffs up its fur and moves less. The RSPCA lists very cold limbs, shivering, pale ears or nose and a hunched posture among the signs a mouse needs a vet, and the MSD manual adds ruffled fur and low energy as general signs of illness. These look the same whether the cause is cold or illness, so warm the room and book a vet if the mouse does not perk up within a few hours. Our pet mouse health guide covers the other signs to watch for, and our pet mouse care guide puts it all in one place.