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How Big Will My Cat Grow Up to Be?

Did you just bring home a new kitten? Are you now wondering: “how big is my cat going to be?” Just like predicting how big your puppy will be, determining how big a cat will be is a bit of a guessing game. A cat’s full-grown size depends on a number of factors such as breed, gender, and lifestyle.

A calico cat sitting in front of a Hale Pet Door for screens


If you know your cat’s breed, that is a pretty good indicator of approximately how big they will grow to be. Smaller cat breeds such as the Cornish Rex may only grow to 8” at the shoulder, whereas a Maine Coon could reach 16” shoulder height! However, for a kitten mixed with “who knows what” adopted from your local shelter, this method of prediction gets a little tricky.


Gender is another factor to keep in mind when considering how big your cat will be. Male cats tend to be larger than females, so you can expect an extra inch or two in most cases.

Nutrition & Activity Level:

While nutrition and activity level generally won’t affect a cat’s height, it can certainly impact their weight. A free-feeding indoor cat is bound to put on a few more pounds than an outdoor cat who spends their days roaming the neighborhood. It’s important to keep a cat’s width in mind when selecting a pet door. Always make sure to measure your pet to ensure the proper fit!

Diagram showing that the step-over plus the flap height should equal a distance that is at least 1

Other Indicators:

Unlike puppies, a kitten’s paw size does not indicate how big they will grow to be. However, tall back legs are often a sign that a cat is going to be bigger than average.

Cats are considered adults when their growth slows between 9 to 12 months. If you have a young kitten at home and you’re wondering about how big they will be, you can try this formula for an estimation:

Weight at 16 Weeks x 2 = Adult Weight

Keep in mind that a cat’s breed, gender, and upbringing will impact their adult weight, making it tough to predict exactly how big they will be.

Choosing a Pet Door:

With all this in mind choosing a pet door might seem daunting. But we are here to help with some options you and your feline friend will love! The Endura Flap has a “high aspect ratio” flap, meaning it is nice and tall in proportion to the width. This allows you to install the door low to the ground for an easy step-over a kitten can maneuver while still being a tall enough flap for them to use into adulthood.

The classic Endura Door Mount and Endura Wall Mount are great options for cats. We would recommend the single flap for most cats, as the double flap can be a bit too heavy for them to push through. See the differences between door and wall mounts here:

Endura Flap single flap pet door for doors in white

Endura Pet Door for Doors

Endura Flap dog door for walls with a single flap in the color bronze

Endura Dog Door for Walls

The small flap size is 6” x 11” to comfortably fit most cats. A note of caution: the Endura Flap is very heavy-duty, and could be tough for a kitten to push through. It’s always an option to remove some magnets from the flap for easier use if needed!

For sliding glass doors, check out the Endura Vinyl Sliding Glass Cat Door. For windows, the Endura Thermo Sash for Cats or the Endura Horizontal Window Cat Door are great options as well.

White vinyl cat door insert for sliding glass doors

Endura Vinyl Sliding Glass Cat Door

Endura Thermo Sash for Cats

The Endura Horizontal Window Cat Door in bronze

Endura Horizontal Window Cat Door

Have more questions about finding the perfect pet door for your cat? We are here to help! Please don’t hesitate to reach out to customer service at any time to answer all your pet door questions.

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