How Big Will My Cat Get Calculator

Worked example

Let's say you have a 16-week-old kitten who weighs 1.8 kg. Here's how the calculation works:

• Weigh consistently

  Weigh your kitten at the same time each week (ideally before breakfast) for the most consistent readings. A kitchen scale works great for small kittens.

• Know your kitten's birthday

  Accurate age is just as important as accurate weight. If you don't know the exact birth date, your vet can estimate age based on tooth development and body condition.

• Consider breed factors

  The formula gives a general estimate. Purebred cats from known large breeds (Maine Coon, Ragdoll, Siberian) often exceed the prediction, while naturally small breeds (Singapura, Munchkin) may be smaller.

• Combine with health checks

  Use this calculator alongside our Cat BMI Calculator for a more comprehensive health picture once your cat reaches adulthood. A healthy weight range depends on both size and body composition.

• Re-calculate as your kitten grows

  The estimate becomes more reliable as your kitten gets older. Try recalculating every 2–4 weeks — the predicted final size should converge to a stable number as your kitten approaches 32 weeks.

Where $\text{Age}$ is measured in weeks.

Understanding the variables

• $\text{Weight}$ — your kitten's current body weight. Can be entered in grams, kilograms, ounces, pounds, or other units.
• $\text{Age}$ — your kitten's current age in weeks. The calculator supports days, weeks, months, or a weeks/days combination.
• $32$ — the assumed age in weeks at which a cat reaches its full adult size.
• $\text{Final size}$ — the estimated adult weight of your cat.

Reverse calculations (bidirectional solving)

One of the most useful features of this calculator is that it works both ways. You can enter any two values and the third will be calculated automatically:

• Final size from age + weight — the standard prediction.
• Weight needed from age + target final size — useful for growth tracking.
• Age from weight + final size — estimate how old your kitten might be if you don't know its exact birth date.

When do cats stop growing?

Many sources say kittens become adult cats after approximately one year of growing. In reality, this varies heavily and ranges from 32 to 52 weeks. Most cats reach their full height and length by 8–12 months, but some breeds (especially large ones like Maine Coons) may continue filling out until they are 3–4 years old.

How big can a cat get?

The biggest domestic cat ever recorded weighed over 21.3 kg (46 lb). The largest feline on earth, a liger named Hercules, weighed over 412.2 kg (922 lb)! Among domestic breeds, the largest are the Siberian cat, Ragamuffin, and Ragdoll. The Guinness World Records longest domestic cat was Stewie, a Maine Coon measuring 123 cm (48.5 in) from nose to tail tip.

Generally, northern breeds that originated in colder climates tend to be larger. It's easier to stay warm when your body surface-to-volume ratio is low — in other words, it's better to be big and round.

How to tell if your cat has stopped growing

If your cat is over 1 year old and shows clear signs of sexual maturity (puberty), you can be almost certain it's an adult. Watch for signs like urine marking, increased affection, and vocalization. If your kitten is younger, use the calculator to estimate the final size.

For more feline health insights, check out our Cat BMI Calculator and Cat Age Calculator.

Cat puberty calculator

Wondering when your kitten will reach sexual maturity? Here's a quick method:

1. Find exactly when your cat was born.
2. Add 6 months for females or 5 months for males.
3. This gives the earliest possible start of puberty. Watch for signs like urine marking, increased affection, and vocalization.