Kitten growth calculator: how big will my cat get?
No source we use gives a formula for a kitten's adult size. This calculator compares your kitten's weight with a 2019 study of kittens from birth to 20 weeks old.
Sex
Pick an age and enter your kitten’s weight to compare it with the study.
A comparison with one study’s averages, not a prediction of adult size. Ask your vet if your kitten’s growth worries you.
Kitten weight by age: the study’s averages
Source: Journal of Feline Medicine and Surgery (2019)
Mean ± standard deviation in kg, as printed in the 2019 study. Birth to 4 weeks: the breeding colony; 6 to 20 weeks: owned kittens.
| Age | All | Male | Female |
|---|---|---|---|
| Newborn | 0.11 ± 0.02 | 0.11 ± 0.02 | 0.11 ± 0.01 |
| 2 weeks | 0.30 ± 0.05 | 0.30 ± 0.05 | 0.29 ± 0.04 |
| 4 weeks | 0.48 ± 0.10 | 0.49 ± 0.1 | 0.47 ± 0.11 |
| 6 weeks | 0.69 ± 0.14 | 0.68 ± 0.14 | 0.71 ± 0.12 |
| 8 weeks | 1.02 ± 0.18 | 1.01 ± 0.18 | 1.03 ± 0.19 |
| 10 weeks | 1.22 ± 0.26 | 1.27 ± 0.31 | 1.18 ± 0.20 |
| 12 weeks | 1.45 ± 0.34 | 1.54 ± 0.38 | 1.36 ± 0.26 |
| 14 weeks | 1.73 ± 0.43 | 1.90 ± 0.46 | 1.55 ± 0.29 |
| 16 weeks | 1.93 ± 0.46 | 2.0 ± 0.49 | 1.82 ± 0.37 |
| 20 weeks | 2.18 ± 0.40 | 2.25 ± 0.40 | 2.13 ± 0.39 |
18 weeks is left out: only 4 kittens were weighed at that age.
How big will my cat get?
Its weight today will not tell you. In a 2022 study of healthy kittens, 28% climbed and 23% fell at least two lines on a growth chart as they grew, so a kitten's place on the chart can change.
The same study linked climbing centile lines with cats becoming overweight by early adulthood, and falling ones with underweight. Weigh your kitten regularly and show the trend to your vet.
How much should a kitten weigh by age?
Shelters often use a rule of 1 lb (0.45 kg) for each month of age. In the 2019 study it matched age within a week for most kittens up to 10 weeks old, and other signs were needed after that.
When do kittens stop growing?
Sources put the end of kittenhood at about one year. ASPCA advises kitten food until a cat reaches maturity at about one year of age, and the AAHA/AAFP kitten stage runs from birth up to 1 year.
Is my kitten underweight or overweight?
Compare it with the study's average for its age and sex. A weight outside the average plus or minus one standard deviation is not a diagnosis, but a kitten that loses weight or stops gaining needs a vet.
The study stops at 20 weeks. For an older kitten, ask your vet to check its body condition; the body condition score chart shows what they look for.
Why does the calculator ask for sex?
Because males and females differ. In the study, males were heavier at 6 and 8 weeks in the breeding colony, and from 10 through 14 weeks in the owned kittens. Pick "Not sure" to compare with all kittens.
Which kittens were in the study?
Two groups: 246 domestic shorthair kittens in a university breeding colony, weighed every 2 weeks up to 8 weeks old, and 1310 owned kittens aged 6 to 20 weeks, weighed once at spay or neuter surgery.
The calculator uses the colony's figures to 4 weeks and the owned kittens' from 6 weeks. It skips 18 weeks, where only 4 kittens were weighed. Most of the owned kittens were domestic shorthairs.
Related tools
Sources
How we choose them- Journal of Feline Medicine and Surgery (2019) — Assessment of body weight for age determination in kittens (PMC full text)
“Body weight was an effective means of predicting age in kittens through 10 weeks of age... using the clinical guideline of 1 lb (0.45 kg) of body weight gain per month of age is the simplest and quickest method available”
- PLOS ONE (2022) — Growth standard charts for monitoring bodyweight in intact domestic shorthair kittens from the USA (PMC full text)
“Crossing centiles in an upwards and downwards direction is associated with cats becoming overweight or underweight by early adulthood, respectively... A total of 142 (28%) and 119 (23%) kittens, crossed at least 2 standard centile lines in an upwards and downwards direction, respectively.”
- ASPCA — Cat Nutrition Tips
“Your pet will need to eat kitten-formula food until she reaches maturity, at about one year of age.”
- AAHA/AAFP — 2021 Feline Life Stage Guidelines
“Kitten: Birth up to 1 year Young adult: 1 to 6 years”