How Small of a Hole Can a Rodent Fit Through?
A gap that looks too small to matter is usually exactly the size a rodent is looking for.
The actual numbers
A mouse can squeeze through an opening about the size of a dime, roughly a quarter inch. A rat needs a bit more, around a half inch, about the size of a quarter. Rodents have flexible skeletons and can compress their bodies significantly to get through gaps that look solid at a glance.
Where these gaps actually show up
Utility penetrations, gaps where two different building materials meet, worn weatherstripping, and warped vent screens are the most common overlooked openings, exactly the kind of gap that gets dismissed as "too small to worry about."
Why this matters for sealing work
Effective rodent exclusion means checking for anything a dime or quarter could pass through, not just the obvious holes. That level of detail is the difference between a seal job that holds and one that does not.