As a general rule kittens gain 1 pound of body weight per month for the first 6 months. Your kitten should be around 1 pounds. Do not be concerned if your kitten is a little bigger or smaller. The individual kitten's body condition score is more important than the actual weight. Vaccines begin at 6-8 weeks of age. Ask your veterinarian at this time to assess the kitten's body condition or sooner if you feel the kitten is ill or underweight.