Kitten Weight Chart by Age, and Adult Cat Weight

In their first weeks kittens gain weight every day, so weight is one of the clues used to estimate the age of a kitten whose birthday isn’t known. The calculator compares your kitten’s weight with the ASPCA Kitten Age & Weight Chart, which gives a normal range for each day from birth to 8 weeks.

Kitten weight chart, weeks 1–8

Week	Age	Start of week (g)	End of week (g)	End of week (oz)
1	1–7 days	70–115	142–190	5.0–6.7
2	8–14 days	149–205	191–295	6.7–10.4
3	15–21 days	198–310	240–400	8.5–14.1
4	22–28 days	247–415	289–505	10.2–17.8
5	29–35 days	296–520	338–610	11.9–21.5
6	36–42 days	345–625	387–715	13.7–25.2
7	43–49 days	394–730	436–820	15.4–28.9
8	50–56 days	443–835	485–925	17.1–32.6

ASPCA Kitten Age & Weight Chart (2023), day 1 and day 7 of each week; the calculator uses every day of the chart. The chart notes that the ranges reflect normal kittens gaining 7–15 g a day, and that weight should be used together with developmental milestones (teeth, eyes) when estimating age. Ounces converted by us.

How the calculator estimates age

It finds every day on the chart whose normal range includes your kitten’s weight and reports the first and last of those days. Because the ranges are wide and overlap, the answer is a window, often two or three weeks long.

Worked examples

Example 1: a kitten weighing 300 g. 300 g fits the ranges for days 15–29, so the kitten is most likely in weeks 3–5.

Example 2: a kitten weighing 8 oz. 8 × 28.35 = 227 g, which fits days 10–19 (weeks 2–3).

Example 3: a kitten weighing 1 lb (454 g). Fits days 25–51, anywhere from week 4 to week 8. At this weight, teeth and eyes say more about age than the scale.

After 8 weeks

The Merck Veterinary Manual gives a normal birth weight of 90–100 g. Kittens grow exceptionally fast for the first 3–4 months, gaining 50–100 g a week. Growth begins to level off at 150–160 days and is usually complete within 200–220 days, at about 7 months.

Adult cat weight

The Merck Veterinary Manual gives the average mature ideal body weight of domestic cats as 3.2 kg (7 lb) for males and 2.8 kg (6 lb) for females. Many pet cats are bigger-framed than that, and some breeds are much larger, so an “average” is a poor target for one cat.

Veterinarians judge a healthy weight with the body condition score (BCS): on the WSAVA 9-point scale, 5 is ideal: well proportioned, with ribs that can be felt under a slight fat covering. Our cat ideal weight calculator explains the scale and estimates a target weight from it.

Limitations

• Weight is only one clue. Litter size, the mother’s nutrition and illness all affect a kitten’s weight. The chart’s own note says to use it with developmental milestones.
• Days 1–56 only. Beyond 8 weeks the chart doesn’t help; ask your vet, who can also examine the teeth.
• The chart has small printing quirks (for example, day 2 starts at 107 g). We use the values exactly as published.