A height, weight and age calculator is a tool used to calculate the body mass index, or BMI, of an individual. BMI is a measure of body fat based on the height and weight of adults over 20 and is used as an indicator of health, explains Medical News Today.
For individuals who are younger than 20, BMI calculations are relative to the age and sex of the person, and therefore cannot be calculated the same way as adults over 20, according to Medical News Today. Calculating the BMI helps individuals determine if they are underweight, average weight or overweight. BMI is not an accurate assessment for individuals who fall outside the norms such as weight lifters or athletes, as these individuals have a higher or lower BMI than average.