Rats are much bigger than mice and produce larger droppings. Mice are small and leave 80+ tiny droppings a night, usually along skirting boards, inside cupboards, or near food sources. If a dropping is larger than the size of a grain of rice, it is more likely to be from a rat; if smaller than 8mm then you likely have mice.
- Brown rats: body length typically 20-25cm (excluding tail); droppings are dark brown or black, capsule-shaped with blunt or slightly pointed ends, around 12-20mm long. Expect heavier scurrying or gnawing sounds in walls, floors, or loft spaces.
- House mice: body length typically 7-10cm (excluding tail); droppings are smaller, dark, and usually 3-8mm long with pointed ends. Mice tend to move more quickly and are generally more curious around new objects.
- Both species reproduce rapidly, contaminate food, and can spread disease, so prompt treatment is important.
Hearing scratching in the walls? Finding small dark droppings in the cupboard? Knowing whether you have rats or mice changes everything - the treatment, the urgency and the entry points to seal. This guide walks through the key differences so you can identify which rodent has moved in.
Rats vs Mice at a Glance
| Feature | Rat | Mouse |
|---|---|---|
| Body length | 20-25cm (plus tail) | 7-10cm (plus tail) |
| Weight | 200-500g | 15-30g |
| Droppings size | 12-20mm, capsule-shaped, blunt or pointed ends, dark brown/black | 3-8mm, dark, pointed ends |
| Droppings per night | Up to 40, concentrated in same spots | Up to 80, spread along skirting |
| Smallest gap they fit through | ~20-25mm (can gnaw bigger) | ~6mm (size of a biro) |
| Sounds heard | Heavy scurrying in walls/lofts | High-pitched scratching, faster |
| Behaviour around new objects | Wary (neophobia) - traps often fail | Curious - sporadic behaviour - traps more effective |
| Diseases carried | Leptospirosis (Weil’s Disease), Salmonellosis, Rat-Bite Fever, Seoul Virus (hantavirus) | Salmonella, Lymphocytic Choriomeningitis |
Size: The Quickest Tell
Adult rats are 20-25cm long in the body, with a tail nearly as long again. They weigh 200-500g and feel substantial. Adult mice are 7-10cm in the body with a slightly longer tail, and weigh just 15-30g. If you spot one and it looks “rat-sized,” it almost certainly is.
Size also tells you about young rodents: a young rat may be mouse-sized, but the head and feet are disproportionately large compared to a true mouse.
Droppings: The Most Reliable Sign
Most rodent problems are identified through droppings before the animal is ever seen.
- Rat droppings are dark brown or black, capsule-shaped with blunt or slightly pointed ends, and around 12-20mm long. A single rat produces up to 40 droppings per night, usually concentrated in the same spots.
- Mouse droppings are much smaller (3-8mm), dark, with pointed ends - similar in size to a grain of rice. A mouse leaves up to 80 droppings per night - often along skirting boards and in cupboards.
Sounds and Behaviour
Rats are heavier and you can usually hear them as scurrying or scratching from under floorboards, in cavity walls, or in lofts. They are wary of new objects in their environment - a behaviour called “neophobia” - which is why DIY traps often fail.
Mice are lighter and faster, with more high-pitched scratching. They are curious rather than cautious, which is why traps can catch them - but their breeding rate (up to 10 litters a year, 14 young per litter) means trapping alone is rarely enough.
Entry Points
Mice can squeeze through a hole as small as 6mm - about the diameter of a biro. Rats need slightly more (around 20-25mm) but can gnaw to enlarge gaps. Both species exploit:
- Gaps under external doors
- Holes around utility cables and pipes
- Damaged air bricks and ventilation grilles
- Gaps in roof eaves and soffits
Rats also burrow next to decking, sheds and patios. Both rats and mice are agile climbers and use cavity walls or climbing plants/overhanging branches to enter at high level.
Health Risk Comparison
Both species spread disease, but rats are the bigger concern. Rats carry Leptospirosis (Weil’s Disease), Salmonellosis, Rat-Bite Fever and Seoul Virus (a strain of hantavirus) through droppings, urine and bites. Mice carry Salmonella and Lymphocytic Choriomeningitis, and contaminate food at scale, but they are less likely to bite humans.
Both can damage electrical wiring through gnawing - a recognised fire risk in lofts and behind appliances.
What to Do Next
If you have identified rats, see our guides to signs of rats and how to deter rats. If it is mice, our signs of mice and how to deter mice guides cover the next steps.
For an established infestation, professional treatment is the only reliable answer. Call our RSPH (BPCA) Level 2 certified and trainee techs for a same-day survey.
Frequently Asked Questions
Can a mouse turn into a rat as it grows?
No - they are different species. Young rats can be mouse-sized but the head and feet are disproportionately large compared to a true mouse. If you see what looks like a “big mouse,” it is most likely a young rat.
Is one easier to get rid of than the other?
Mice are slightly easier to catch with traps because they are curious. Rats are warier and a single bad trap placement can train the rest of the colony to avoid it. For established infestations of either species, professional treatment is far more reliable than DIY.
How quickly does an infestation get worse?
Faster than most people expect. A female mouse can produce up to 10 litters of 14 young in a year. Rats breed slightly slower but live in larger colonies. Acting within days of spotting droppings is far cheaper than acting weeks later.
Do droppings always mean an active infestation?
Not necessarily - droppings can be old. Fresh droppings are dark, soft and shiny; old droppings are grey, dry and crumbly. To check if the problem is still active, clear the droppings, wait 24-48 hours and look for new ones.
Are rats or mice more dangerous to my pets?
Both can transmit diseases to pets through bites or contaminated food and water. Rats are the bigger health risk because of Leptospirosis (dangerous to dogs especially). DIY rodent poisons are a far greater risk to pets than the rodents themselves - which is one reason professional bait stations are tamper-resistant.