Kitten Development Calculator
Track your kitten’s growth with this free kitten development calculator. Estimate a kitten’s age from its weight, follow the week-by-week milestones, see the kitten weight chart by age, predict the adult size, and convert kitten age into human years — all in one tool.
How the Kitten Development Calculator Works
The five tools cover age from weight, the week-by-week developmental timeline, an adult-weight predictor with breed ranges, a weight chart by age, and a kitten-to-human age converter.
Kitten Growth Chart: Weight by Age (Week by Week)
This kitten weight chart shows the typical weight at each age for an average domestic cat, from birth to one year. Ranges are wide because sex, breed and litter size all matter — use it to check that your kitten is tracking upward, not to hit an exact figure.
| Age | Weight (grams) | Weight (oz / lb) | What’s happening |
|---|---|---|---|
| Newborn | 70–130 g | 2.5–4.5 oz | Eyes & ears closed, nursing |
| 1 week | ~150–250 g | ~5–9 oz | Eyes beginning to open |
| 2 weeks | ~200–300 g | ~7–10 oz | Eyes open, ears opening |
| 3 weeks | ~280–400 g | ~10–14 oz | First baby teeth, first steps |
| 4 weeks (1 mo) | ~350–450 g | ~0.8–1 lb | Walking, weaning starts |
| 6 weeks | ~500–700 g | ~1–1.5 lb | Weaning, litter training |
| 8 weeks (2 mo) | ~800–1000 g | ~2 lb | Fully weaned, first vaccines |
| 12 weeks (3 mo) | ~1.1–1.5 kg | ~2.5–3.5 lb | Socialisation peak |
| 16 weeks (4 mo) | ~1.6–2.2 kg | ~3.5–5 lb | Adult teeth coming in |
| 6 months | ~2.3–3.2 kg | ~5–7 lb | Near spay/neuter age |
| 12 months | ~3.6–4.5 kg | ~8–10 lb | Adult size (most breeds) |
Kitten Development, Week by Week
A kitten packs more change into its first two months than any other time of life. In the first week it is a blind, deaf newborn that can only nurse and sleep. Its eyes open between days 7 and 14, always blue at first, and the ear canals open around the same time. By three weeks the first baby teeth appear and it takes wobbly first steps; by four weeks it is walking, playing and ready to start weaning onto wet kitten food. Between five and six weeks the eye colour begins shifting from blue to its adult shade, all 26 baby teeth are in, and litter training clicks. By eight weeks (two months) the kitten is fully weaned, litter-trained, weighs about two pounds and is ready for its first vaccinations.
The socialisation window peaks between about two and nine weeks — gentle handling, new sounds and positive experiences in this period shape a confident adult cat, which is one reason many rescues keep kittens with their littermates until 12 weeks rather than rehoming at eight. From three to six months the 30 adult teeth replace the baby set and the kitten keeps gaining roughly a pound a month, reaching the usual spay/neuter window around five to six months. Growth then slows through adolescence, and most domestic cats are near their adult size by 12 months.
How Much Weight Should a Kitten Gain Per Day?
A healthy young kitten should gain weight every day, averaging about 7 to 14 grams (roughly a quarter to a half ounce) a day, which works out to around 50 to 100 grams a week in the first few months. A useful shorthand many fosterers use is about 100 grams, or a quarter pound, a week — and the classic rule that a kitten gains about one pound a month until roughly five months. Day-to-day weight bounces a little, so what matters is the trend on a weekly weigh-in, not a single reading. A kitten that stops gaining, or loses weight across several days, is a red flag: contact a vet promptly, because very young kittens can decline quickly. A kitchen or jewellery scale that reads in grams is the single most useful tool for tracking a kitten’s growth.
How to Tell How Old a Kitten Is
When you find a stray or take in a rescue, four physical signs pin down the age. Weight is the fastest clue — at roughly a pound per month, a 1 lb kitten is about four to five weeks, a 2 lb kitten about eight weeks. Eyes: closed means under a week; open and blue means one to six weeks; the colour starting to change means six weeks or more. Ears: flat and folded in the first week, then unfolding and standing up by about three weeks. Teeth are the most reliable: the first tiny incisors appear around two to three weeks, the baby canines by four weeks, a full set of 26 baby teeth by six to eight weeks, and the adult teeth coming in from three to four months. Put the weight estimate from the calculator together with these signs for a confident age.
How Big Will My Kitten Get? (Adult Weight)
The most reliable home method is the 16-week rule: a kitten is roughly half its adult weight at four months, so doubling the 16-week weight gives a good adult estimate. A kitten that weighs four pounds at 16 weeks is likely to finish near eight pounds. The calculator applies this across the whole growth curve and blends it with the typical range for the breed you choose. Most domestic cats land between 8 and 10 pounds and reach adult size by about a year. Breed changes the picture a lot: Siamese and many domestic cats stay in the 8–10 lb range, while Maine Coons (13–18 lb), Ragdolls (12–20 lb) and British Shorthairs are far larger and keep growing until 18 months to 3–4 years. Neutering, diet and genetics all nudge the final weight, so treat any projection as a guide rather than a guarantee — and feed a growth-formula kitten food until your vet advises the switch to adult food.
Frequently Asked Questions
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