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What Size Hole Can a Rat Get Through?

Rowan Burgess |

Rodents pose issues for businesses, residential properties, and more. You'll find larger populations in areas of higher human activity. There are two main species of rat that you're likely to encounter.

Rattus norvegicus are common rats found on streets, in common areas, and in homes, whereas Rattus rattus are black and often found in roofing. Rodents have evolved specific physical characteristics to flourish, breed, and fit through tiny holes and underdoors.

Do Rats Have Bones?

Yes, rats have bones. Rats are members of the rodent family, and, like all mammals, they possess a skeletal system consisting of various bones connected by joints and cartilage. This bony structure is similar to that of other mammals, and it facilitates various bodily functions.

How Rats Fit Into Small Spaces

Body Structure

Rats have long, cylindrical bodies well-suited for navigating tight spaces. This streamlined body shape allows them to easily squeeze through narrow openings that might seem too small for their size. This elongated body form is a significant adaptation that supports their burrowing and exploratory lifestyle.

Skeletal System

Rats possess a typical mammalian skeletal system, featuring a network of bones interconnected by joints and cartilage, similar to other mammals. Their bones are neither collapsible nor highly flexible. What distinguishes rats is their notable lack of collar bones, which plays a pivotal role in enhancing their overall flexibility. 

This unique skeletal arrangement, when coupled with their elongated body shape, grants them the remarkable ability to infiltrate confined spaces with ease. Rats' distinctive skeletal structure, devoid of clavicles, effectively complements their streamlined physique, enabling them to navigate through narrow crevices and tight passages.

Not only that, but it's easy for rats to gnaw through various materials; indeed, their dentition is specialised for gnawing. 

Behavioural Adaptations

Rats display distinct behavioural adjustments that facilitate their passage through narrow openings. They employ their extended, sensitive noses and whiskers to gauge the dimensions of an opening, ensuring it's sufficiently wide for safe passage. 

This reliance on sensory feedback prevents them from becoming trapped or misjudging their movements in tight spaces. Furthermore, their innate tendency to explore along walls and enclosed spaces, described as thigmotaxic, is an instinctual behaviour that enhances their proficiency in navigating confined areas. 


The size of a rat can also influence its ability to fit into small spaces. Common rat species, such as the Norway and Roof rat, typically measure around 22 to 27 centimetres in length (excluding the tail). However, juvenile rats are considerably smaller, and their ability to squeeze through even tinier spaces is remarkable.

Soft Skull

Rats have relatively soft skulls; they are not fully fused and may have weak spots, particularly in younger rats. This feature allows them to apply pressure and slightly deform their skull to fit through tight spaces. 

So, How Small of a Hole Can a Rat Fit Through?

Rats are remarkably adept at squeezing through small openings, but the size of the hole they can fit through depends on several factors. While there is no fixed measurement due to age, size, and physical condition, we can provide a general idea of the hole size a rat can fit through.

Under optimal conditions, an adult rat typically requires a horizontal gap of approximately 12mm (about half an inch) and a round hole with a diameter of around 25mm (about one inch) to pass through comfortably. However, young rats, particularly those freshly weaned, can fit through much smaller openings due to their smaller size.

It's crucial to consider factors such as the orientation of the hole (horizontal or round), the rat's ability to gain grip and purchase to push its body through, the height of the hole from the ground, and the type of substrate the hole is in. Holes located halfway up a wall or in areas that are challenging to access may require slightly larger openings, as rats may find it more difficult to fit through in less optimal body positions or with less leverage from their legs.

How To Seal Small Spaces From Rats

Identify and Inspect Potential Entry Points

Conduct a thorough inspection of your property, both indoors and outdoors, to identify potential entry points for rats. Common areas to check include gaps around doors and windows, holes in walls or floors, spaces around pipes and vents, cracks in the foundation, and gaps in roofing or eaves.

Choose the Right Materials for Sealing

You'll need suitable materials and rodent control products to seal small spaces from rats. Steel Wool is an excellent choice, as rats dislike chewing on steel wool due to its roughness and ability to harm their teeth. It's ideal for filling small holes and cracks. We also recommend hardware cloth, a metal mesh with small openings suitable for covering larger vents and chimney openings.

Other options included caulk and cement. Ensure that the materials you choose are sturdy and resistant to gnawing, as rats have strong teeth that can chew through many materials.

Seal the Holes and Gaps

Pack holes tightly to prevent rats from pushing through. Larger holes may warrant a mixture of sealants, like cement and steel wool. Mix the cement as directed and insert steel wool into the opening before applying the cement.

Secure hardware cloth with screws or heavy-duty staples and positioned over vents or larger openings. Take care to inspect your home thoroughly and routinely. Learning how to get rid of rats involves looking for new gaps or evidence of rat activity, such as droppings or gnaw marks. Maintaining vigilance will help ensure your home remains rat-free.

Frequently Asked Questions

Can a Rat Fit Under a Door?

Young, small rats can fit through gaps under doors. It’s important to fix protective strips on the bottom of doors to serve as a deterrent. Rats can also fit through cat flaps and will gnaw at vulnerable areas to enter a property.

Looking for Rodent Control? Shop Dalton Engineering!

Rats' body adaptations, including long, flexible, collar bone-free bodies, enable them to fit through various openings. To prevent infestations, inspect your property, seal gaps with materials like steel wool or hardware cloth, and maintain proper door seals. 

Shop Dalton Engineering for rodent control products and rid yourself of rodent issues today!