Find online calculators for determining a person's weight or body mass index on sites such as CDC.gov, NHS.uk, NIH.gov and MayoClinic.org. Body mass index is a formula that compares people's weight to their height based on a predetermined chart of ratios.
Most online weight and body mass index calculators ask a user to input her height, weight and gender in order to determine her position on the body mass index chart. These values do not take into account other factors about the person's health and body. They serve only as a general guideline based on statistical data. Body mass index generally determines if a person is underweight, overweight or has a healthy weight.