When Are Cats Full-Grown?

As a cat parent, it's hard not to think of your kitty as a baby, even when they're well into their golden years. Because many cats retain their youthful behavior well into adulthood, it makes you wonder, when are cats full-grown adults and at what age are cats full-grown? Age and breed play a large part in when a kitten becomes a cat.

When Are Cats Full-Grown?

One day, you have a tiny kitten running around your house, and before you know it, they're a big cat. It may seem like they grow overnight, but cats actually go through five life stages, as explained by the American Association of Feline Practitioners and American Animal Hospital Association life stage guidelines. One way to determine when your cat is full-grown is to see into which category they fall into:

• Kitten (birth to six months)
• Junior (six months to two years)
• Prime (three to six years)
• Mature (seven to 10 years)
• Senior and geriatric (11 years and up)

Much like their human counterparts, the development stages of kittens are counted in weeks and months up until the age of two. At what age are cats full-grown? At about one year old. Cats reach adulthood in the junior stage moving into prime stage. You can think of this as your cat being in their late teens and 20s, young adults full of energy and verve.

Once your cat ages into adulthood, your veterinarian can help you determine your cat's ideal weight and recommend a meal plan to help optimize their health. You can work together to modify this plan as your cat moves into each new life stage. It's important to schedule this visit so that these baselines can be established, allowing you to keep an eye on your cat's wellness as they age.

How Do Gender and Breed Affect a Cat's Size?

Once your cat is officially a grown-up, they reach their full size. A cat's size is determined by their genetics: The average house cat weighs between six and 12 pounds and is about 18 inches long and 10 inches tall. A cat's weight may fluctuate as they age, but physical traits such as size, as well as eye color, body length, coat pattern and texture, are fully developed by the age of two. Generally speaking, male cats are larger than female cats in height, length and weight. This is common among mammals, reports Science Daily, and researchers chalk it up to natural selection.

Depending on their breed, some cats are smaller or larger than average once they're full-grown. The Merck Veterinary Manual notes that "only 5 to 10 pounds separate the smallest and largest domestic breeds of cats," but when you're talking about small creatures like the house cat, that's a big difference. There are many cat breeds throughout the world. The International Cat Association recognizes 71 pedigree breeds as well as mixed breeds — each of which comes with its own size determinations.

Keep in mind that the weight of average cats is determined based on cats of a healthy weight and body condition score. Overweight or underweight cats may differ from these averages, so it is always good to speak to your veterinarian about what a healthy weight should be for your particular kitty to ensure they remain as healthy as possible.

Pedigree and Mixed-Breed Cats

If your cat is a pedigree breed, you have a better sense of what their full size will be, points out the Cornell Feline Health Center at Cornell University, but with a mixed breed, it's difficult to know for sure. If you adopt a certified pedigree breed like the Maine Coon, for instance, you know you're getting a large furry friend — male Maine Coons can weigh up to 25 pounds and measure up to 40 inches long! On the flip side, the smallest cat breed, the Singapura, weighs at the most eight pounds and only measures around eight inches tall and 12 inches long. Not only is the Singapura smaller, but they also reach adulthood later, around two years of age.

Mixed breed cats are a wonderful amalgamation of multiple breeds that create a unique cat, and you never know what you're going to get! It's fun to see what dominant traits your mixed-breed kitty acquires as they grow into an adult.

If you've raised your cat from a kitten or the junior stage of life, you have a pretty good idea of their temperament and social-emotional needs. You also know their favorite napping spot and favorite toy. As your furry friend grows up, you also want to ensure that they have a well-balanced, nutritious meal plan that's formulated for their age range, so they get the vitamins and nutrients they need.

Contributor Bio

Christine O'Brien

Christine Brovelli-O'Brien, Ph.D., is an award-winning writer, editor, and long-time cat mom. She's a professional member of the Cat Writers' Association (CWA) and has written for industry-leading companies and organizations, including What to Expect When You're Expecting and NIU STEM Read. Find and follow Christine on Instagram and Twitter @brovelliobrien