There is no clear consensus on the correct definition of ideal body weight (IBW) in children or on the best method used to calculate IBW. There are at least 3 ways of obtaining IBW in children. They are (1) the McLaren method, (2) the Moore method, and (3) the body mass index method. In children under the age of 8 years, all of these methods provide relatively similar results across all percentiles. In older children, especially at the lowest and highest percentiles, the different methods provide widely disparate results for IBW. It is important to be consistent in the method used as the different methods will provide different results for IBW.