A small brown house mouse sitting beside a skirting board on a wooden kitchen floor in soft morning light
AI-generated image, not a photograph of a real person or place.
doodlemice

WHAT THE GUIDANCE SAYS

A gap the width
of a pencil.

5 MM is enough

  • Look for droppings
  • Seal gaps round pipes
  • Food in sealed tubs
  • Small gaps, small habits

That is all a house mouse needs to get in.

House mice come indoors all year round for food and shelter, and their numbers can rise quickly. UK council environmental health teams agree on the signs to look for and the gaps worth sealing.

Updated

Check the signs

THE SHORT ANSWER

Find the signs,
close the gaps.

Mice come in for food and shelter.
Take away both and they look elsewhere.

THE SIGNS

Droppings come first

Droppings are black, rod-shaped and 3 to 6 mm long. Watford Borough Council says they are often the first sign of mice.

Check the signs

THE GAPS

Seal round pipes and doors

Councils say to seal gaps around heating and water pipes and fit brush or bristle strips under external doors.

Proofing steps

THE FOOD

Out of reach, lids on

Store food off the ground and keep opened packets in sealed or airtight containers. Close bin lids and composters.

See the numbers

A QUICK SIGNS CHECK

What have
you found?

Pick what you have noticed to see what councils say it means. The bar shows how strongly it points to mice.

Signs check

Choose what you found
Scratching in the ceiling at nightPossible

Councils list noises in wall cavities, voids and across ceilings as a sign. Look for droppings in the loft or roof space to confirm.

Dark greasy marks along a skirtingLikely runs

Smear marks are dark grey marks left by the oils in mouse fur as they brush along the same routes.

Shredded paper in a cupboardPossible nest

Mice build nests from paper, cloth, wool and plastic, often in lofts, under floorboards or in airing cupboards.

A nibbled cereal packetStrong sign

Gnawed food packets are a classic sign. Mice also gnaw wood, carpets, skirting boards and electrical cables.

Small black droppingsStrong sign

Droppings 3 to 6 mm long, black and rod-shaped, often under the sink or around the boiler. Fresh ones are soft and moist.

Sources: Birmingham City Council, Burnley Borough Council, Mid and East Antrim Borough Council and Watford Borough Council mice advice.

Based on UK council environmental health advice. If unsure, contact your council's environmental health team.

TWO NUMBERS WORTH KNOWING

Small animal,
big numbers.

One figure on how many signs one mouse leaves,
one on how fast a few become many.

≈ 80 a day

Droppings left by one mouse in a day

Burnley and Mid and East Antrim councils say each mouse can leave approximately 80 droppings per day, which is why droppings are often the first thing people notice.

DROPPINGS · UK COUNCILS

5–10 a year

Litters a house mouse can have each year

Birmingham City Council says mice produce 5 to 10 litters a year with about 4 to 8 young in each, and typically live 10 to 24 months.

BREEDING · BIRMINGHAM CITY COUNCIL

Councils give slightly different gap sizes: about 5 mm (Burnley, Mid and East Antrim), 6 mm (Watford) and about 1 cm, the size of a 1p coin (Birmingham). All agree that very small holes are worth filling.

FOUR PROOFING STEPS

Keep them out
for good.

Pasta, cereal and rice stored in clear airtight containers on a tidy kitchen shelf
AI-generated image, not a photograph of a real person or place.

Mouse-proofing is mostly about small gaps and easy food. These steps come from UK council environmental health advice.

  1. Brush strips on outside doors

    Fit draught-excluding brush or bristle strips to close gaps under external doors.

  2. Fill holes round pipes

    Block holes around pipes with wire wool or mesh, then fill with cement or expanding foam.

  3. Mesh the vents, never block them

    Replace worn vent mesh with fine 3.15 mm insect mesh. Watford warns not to block air vents.

  4. Trim plants by the eaves

    Cut back foliage touching the roof so mice cannot climb into the loft, and keep gardens tidy.

FOOD AND BINS

Nothing to
find, nothing to stay for.

A hand fitting a brush draught strip to the bottom of a back door, closing the gap above the threshold
AI-generated image, not a photograph of a real person or place.

Mice are drawn by food and by shelter for nesting. Councils advise storing food off the ground, keeping opened packets in sealed or airtight containers, and regularly cleaning food debris from cookers, fridge-freezers and microwaves.

Outside, close dustbin lids and composters, move household rubbish out regularly, and use a proper bird feeder, because mice may feed from spilled seed too.

Questions

Questions people ask

How small a gap can a mouse get through?

Burnley and Mid and East Antrim councils say cracks as small as 5 mm, or a gap the diameter of a pencil. Watford gives 6 mm and Birmingham about 1 cm, the size of a 1p coin.

Do mice only come in during winter?

No. Watford Borough Council says mice enter buildings all year round, drawn by food and shelter.

How do I tell mouse droppings from rat droppings?

Councils describe mouse droppings as black, rod-shaped and about 3 to 6 mm long, like small grains of rice. If you are unsure what you have found, your council's environmental health team can advise.

How big is a house mouse?

Burnley Borough Council says house mice weigh less than 25 g, with a body 60 to 90 mm long and a tail adding about 100 mm.

Will my council help?

It varies. Burnley offers free treatment for mice at homes; Birmingham gives free advice but no mouse treatment service. Check your own council's environmental health pages.

Sources

Where the facts come from

  1. Birmingham City Council: Advice leaflet, mice
  2. Burnley Borough Council: Mice
  3. Mid and East Antrim Borough Council: Mice
  4. Watford Borough Council: Mice information sheet

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