Calculate the ideal weight for your baby using a body-mass index indicator available on websites such as WebMD. This calculator requires the child's sex, birth date, height and weight, as well as optional information such as the mother and father's height, explains WebMD. The results fall into underweight, healthy weight, overweight or obese ranges, indicating the health level of your child's weight.
Alternatively, use growth charts available on websites such as Parents.com to calculate your child's ideal weight. This chart helps you determine your child's height and weight percentile using research data from the Centers for Disease Control and Prevention. Use the growth chart by entering your child's gender, height in inches, weight in pounds, age and birth date. However, to receive full results from this chart, you must provide an email address and create a password, but can opt out of receiving emails.
Other websites that offer children's growth charts to calculate ideal weights include About.com and the Centers for Disease Control and Prevention, with the CDC requiring the most information and providing the most extensive results. The CDC separates charts for infants from birth to 36 months, children and adolescents from 2 to 20 years, and children from 2 to 5 years for parents who want only a weight and stature comparison chart, according to its website.