A healthy kitten weighs about 3-4 ounces at birth. This is 100-125 grams. They should double their birth weight within 2 weeks. This is an average. Some modern cat breeds such as the Maine Coon and Savannah cat (F1s and F2s) will weigh more as the former is the largest domestic cat breed and the latter is the largest domestic cat but a wildcat hybrid.
If the birth weight of a kitten is 25% less than the weight of littermates they are unlikely to survive unless placed in an incubator to be raised by hand.
Further, kittens with a birth weight of 90 grams (3 ounces) or less are more likely to die early. At five weeks their weight should be about one pound (454 grams) and at ten weeks of age, 2 pounds (907 grams).
Consistent weight gain is a good indicator of health. Conversely a failure to gain weight is concerning. Healthy kittens gain weight at about 7-10 grams daily.
My thanks to the vets and authors of the Cat Owner’s Home Veterinary Handbook at page 457 and 459 of the 3rd edition.
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