How Big Will My Cat Get?
Estimate your kitten's grown-up size. Enter its current weight (lb or kg) and age in weeks to project an adult weight, using the classic rule that a kitten is about half its adult weight at 16 weeks. It is a rough guide, not a guarantee.
Example: with Current weight 4 · Weight unit pounds (lb) · Age (weeks) 16 → Estimated adult weight: 8 lb (3.6 kg).
- Likely adult range6.8 to 9.2 lb
- How that comparesAverage-size adult cat (~8 to 12 lb range)
Computed by the calculator below using its default values. Change any input to see your own numbers.
A common breeder rule of thumb: a kitten is roughly half its adult weight at 16 weeks (4 months), so doubling the 16-week weight approximates the adult size.
What the 16-week rule really tells you
Breeders often say to weigh a kitten at 16 weeks and double it for a rough adult weight. That works because most domestic cats reach about half their final weight around four months, then slow down and finish growing between 10 and 18 months. This tool generalizes that idea: it estimates what fraction of adult size a kitten of a given age has reached, then divides to project the finish line.
Treat the number as a ballpark. Breed, genetics, sex, and neutering all shift the outcome, and the estimate widens for very young kittens. A Maine Coon or Ragdoll can keep growing for years, while a petite domestic shorthair may top out below the average.
How it’s calculated
Adult weight = current weight ÷ the estimated fraction of adult size for the kitten's age, interpolated from a rough guide anchored at 50% at 16 weeks (the classic doubling rule). Kilograms convert at 1 kg = 2.20462262 lb. The likely range is the estimate ±15%.
A rough breeder and vet rule of thumb, not a growth chart for your specific cat; individual kittens vary widely. Ask your veterinarian about healthy weight and body condition for your breed.
Rough share of adult weight by kitten age
| Age | ~% of adult weight | If adult is 10 lb |
|---|---|---|
| 1 mo (4 wk) | 13% | ~1.3 lb |
| 2 mo (8 wk) | 25% | ~2.5 lb |
| 3 mo (12 wk) | 38% | ~3.8 lb |
| 4 mo (16 wk) | 50% | ~5.0 lb |
| 6 mo (24 wk) | 70% | ~7.0 lb |
| 8 mo (32 wk) | 82% | ~8.2 lb |
| 10 mo (40 wk) | 90% | ~9.0 lb |
| 12 mo (52 wk) | 97% | ~9.7 lb |
Rough breeder and veterinary guideline; individual kittens vary. The 16-week point anchors the classic doubling rule.
Common mistakes
- Trusting the estimate for a 6- or 8-week-old kitten, where the range is very wide.
- Forgetting that big breeds like Maine Coons keep growing well past a year.
- Confusing a chubby kitten for a large-breed one — extra weight is not the same as a bigger frame; ask your vet about body condition.
Frequently asked questions
How do I estimate my cat's adult size?
Weigh your kitten at 16 weeks and double it for a rough adult weight, or enter any age here to project from a growth-share guide. Most cats reach about half their adult weight by four months.
How accurate is the 16-week doubling rule?
It is a decent ballpark for average domestic cats but only a rule of thumb. Breed, genetics, and sex can push the real adult weight well above or below it.
When do cats stop growing?
Most domestic cats finish growing between 10 and 18 months. Large breeds such as Maine Coons and Ragdolls can keep filling out for two to four years.
My kitten seems small or large for its age — should I be concerned?
A single weight is not a diagnosis. Ask your veterinarian to assess growth and body condition, especially if your kitten is far off the typical range.