Mice can squeeze through any gap roughly a quarter inch wide, about the width of a pencil. Keeping them out comes down to three things: sealing every opening they could use, removing the food and shelter that attract them, and catching any that slip through. Here’s how to do each one effectively.
Find and Seal Entry Points
A full inspection of your home’s exterior is the single most effective thing you can do. Mice compress their bodies to fit through remarkably small spaces, so you’re looking for any crack, gap, or hole a quarter inch or larger. Common spots include where utility pipes and wires enter the foundation, gaps around dryer vents, spaces under doors, cracks where siding meets the foundation, and openings around window-mounted air conditioners.
Inside, check behind appliances, around plumbing under sinks, and where pipes pass through walls or floors. Gaps around the edges of garage doors are another frequent entry point. Do your inspection in daylight and look for light coming through from outside. Also look for physical signs of mice: small dark droppings, greasy rub marks along walls, or bits of chewed material.
Best Materials for Sealing Gaps
Mice chew through most soft materials easily, so what you seal with matters as much as finding the hole. Steel wool is the classic choice because its sharp edges poke mice in the nose and damage their teeth when they try to gnaw through. On its own, though, steel wool can rust and fall out over time. The more durable approach is to stuff a small amount of expanding foam into the hole, press steel wool into the foam while it’s still wet so the two bond together, then finish with a sealant that matches the surrounding surface.
Copper mesh is another strong option. It’s tightly woven, corrosion-resistant, and virtually indestructible, making it a better long-term choice than steel wool in damp areas like crawl spaces or around outdoor plumbing. For larger holes in masonry, hydraulic cement or metal flashing gives you a permanent fix. The key principle: the final barrier needs to be something a mouse can’t chew through.
Eliminate Food Sources
Mice are determined scavengers. They’ll chew through paper, cardboard, and plastic food packaging without much effort. The most effective storage containers are metal, such as metal canisters with tight lids or metal bins for bulk goods like pet food and birdseed. Thick glass jars with screw-top lids also work well. If you store dry goods in your pantry in their original bags or boxes, you’re essentially leaving an open invitation.
Beyond the pantry, keep counters and floors free of crumbs, store pet food in sealed containers overnight, and take garbage out regularly. A kitchen that looks clean to you can still feed a mouse for days on crumbs behind the stove or grease residue under the burners. Pull out large appliances once or twice a year and clean behind them.
Manage Your Yard and Exterior
The area around your foundation creates the staging ground mice use before finding a way inside. Firewood stacks, wooden pallets, and landscape timbers should not be placed against or near your house. These provide perfect shelter for mice and other rodents to nest in before they discover a gap in your wall. The same applies to compost bins, which should be set well away from any structure.
Trim any tree branches or shrubs that touch or overhang your house. Roof rats can jump three feet vertically and more than four feet horizontally, so branches that seem “close but not touching” may still serve as a launchpad onto your roof. Dense ground cover or heavy mulch right against the foundation also gives mice cover. Keep a clear zone of at least a foot between plantings and exterior walls where possible.
Set Traps the Right Way
If mice are already inside, trapping is the safest and most immediate way to deal with them. Use snap traps sized for mice, not the larger rat traps. Mouse-sized traps fit more easily along baseboards, behind appliances, and in the narrow paths mice actually travel.
Placement matters more than bait. Position the trigger end of each trap flush against the wall or baseboard, because mice travel along edges rather than crossing open floor. In narrow passages like the gap behind a refrigerator, placing traps on both sides of the path improves your chances. Put multiple traps wherever you see the most droppings or other signs of activity.
For bait, use a very small amount of something sticky like peanut butter, pressed directly into or onto the trigger plate. A large glob of bait actually makes the trap less effective because a mouse can nibble at the edges without pressing down on the trigger mechanism. You want the mouse to step onto the trigger to reach the food. Check traps daily and reset or move them if they’re not getting results after a few days.
Why Peppermint Oil and Ultrasonic Devices Don’t Work
Peppermint oil and ultrasonic plug-in repellers are widely recommended online, but neither provides reliable, long-term mouse control. Peppermint oil’s strong scent can mildly irritate mice and temporarily mask odor trails, but it dissipates quickly. It has minimal measurable impact on rodent behavior and scientific evidence does not support it as a standalone repellent.
Ultrasonic devices face similar problems. Mice may avoid the sound initially but quickly habituate to it, especially when food and shelter remain available. The sound waves also don’t travel well through walls or furniture, creating dead zones where mice simply hide unaffected. You might notice fewer mice in one room for a few days, but the problem just moves rather than resolves. Neither method replaces physical exclusion and proper sanitation.
Be Careful With Rodenticides
Poison bait stations might seem like an easy fix, but they carry real risks. The most potent single-dose rodenticides are restricted to licensed pest control professionals and aren’t available over the counter. The products you can buy as a homeowner are typically slower-acting anticoagulants, and these create a secondary poisoning risk: a cat, dog, or owl that eats a poisoned mouse can be poisoned in turn. Compounds like bromadiolone and brodifacoum pose especially high secondary poisoning risks to pets and wildlife.
If you have pets, small children, or wildlife you care about in your area, snap traps are a safer choice. They kill instantly without introducing toxins into the food chain. If you do use bits, always place them inside tamper-resistant bait stations and follow label directions exactly.
How to Clean Up After Mice Safely
Mouse droppings, urine, and nesting material can carry pathogens, including hantavirus in some regions. The most important rule: never sweep, vacuum, or blow compressed air on dry droppings. These actions launch contaminated dust into the air, which is the primary exposure pathway for infection.
Instead, put on rubber or plastic gloves, then spray the droppings and surrounding area thoroughly with a disinfectant or a bleach solution. Let the material soak for the recommended contact time (usually five to ten minutes), then wipe everything up with paper towels or disposable cloths. Bag the waste, seal it, and dispose of it according to your local guidelines. Clean and disinfect the surrounding surfaces, then wash your hands after removing gloves.
For enclosed spaces like sheds, garages, cabins, or storage rooms that have been closed up, ventilate the area first by opening doors and windows for at least 30 minutes before you start cleaning. If you’re dealing with a heavy infestation, contaminated ductwork, or dead rodents in hard-to-reach places, that’s a situation for professional pest control or your local public health department rather than a DIY project.