Use the free Kitten Adult Weight Predictor below, right in your browser. No sign-up, no software to install, and nothing is sent to a server.
Every kitten owner asks the same question sooner or later: how big will my kitten get? The Kitten Adult Weight Predictor gives a reasoned answer from two numbers you already know, age and current weight. It uses a growth curve, which is simply the share of adult size a kitten has usually reached at each age.
The idea is simple. A kitten is not a small adult; it grows in a curve that is steep at first and flattens near one year. At 8 weeks a kitten is roughly a fifth grown, at 16 weeks about half grown, and at 9 months about nine tenths grown. Divide the current weight by that share, and you get an estimate of the adult weight.
To use the tool, enter the age in weeks and the weight in grams, then choose male or female. Males usually finish a little heavier than females, so the tool adds a small adjustment for males. Press the button and you get an adult weight in grams and kilos, plus how grown your kitten already is.
Try the default example. A 16 week old female kitten weighing 1200 grams is about half grown, so the estimate is 2400 grams, or 2.4 kilos. That is a typical small to medium adult cat. If the same kitten were male, the estimate would be a little higher, near 2.6 kilos, because males tend to carry more muscle and bone.
Predictions are most useful between 8 and 26 weeks. Very young kittens vary a lot, because a few days of age or a small weighing error changes the share a lot. After one year the tool simply returns the current weight, since growth is basically done, even though some large breeds fill out slowly until 18 months.
Breed is the biggest reason a prediction can miss. A Maine Coon or a Ragdoll can finish far above the average, while a Siamese or a Singapura stays small. Mixed breed kittens from unknown parents are harder still, because you cannot see the parents for a clue. Treat the result as a central guess with a range of half a kilo either way.
Weighing well makes the prediction better. Weigh in grams on a kitchen scale, before a meal, and use the same scale each time. Weighing in whole kilos rounds away the detail this maths needs, and weighing after a big meal can add 50 grams that the tool reads as real growth.
Repeat the prediction once a month and watch how it moves. If each new prediction lands near the last one, your kitten is growing on a steady track. If the estimate jumps up or down sharply, check the weighing first, then feeding, then ask a vet whether growth looks normal for your kitten.
This tool is educational only. It does not diagnose growth problems, and it cannot tell you whether your kitten is underweight or overweight. A vet who can see and feel your kitten will always give better advice than any curve, especially if growth seems slow, fast, or uneven.
Use the estimate for practical plans: carrier size, food amounts as an adult, and how much space a full grown cat will need. Then keep enjoying the kitten stage, because it passes fast. One weighing a month keeps the prediction honest, and the answer gets more accurate as your kitten grows.
Parents and littermates give extra clues when the maths alone feels uncertain. If you met the mother, her adult size is a strong hint, since kittens often land near the mother size, with males a little above it. Littermates help too: a kitten that is clearly the largest of its litter usually stays above average, while the smallest often stays small. Combine these clues with the tool result, and you get a range you can trust for practical plans like carrier size and adult food amounts.
Versión en español: Predictor de peso adulto de gatitos – Estimación por edad y peso