A body mass index calculator is a simple program that calculates a person's BMI based on the person's height and weight. The basic formula is weight in pounds divided by the square of the height in inches, then multiplied by 703.
The BMI is a tool that assesses a person's level of body fat. The normal range is 18.5 to 24.9. Results below 18.5 suggest that the measured individual is underweight and may be malnourished. Results from 25 to 29.9 suggest overweight, and a result over 30 indicates obesity.
BMI is only a rough guide to physical condition and can give misleading results in very muscular individuals, as muscle weighs more than fat per unit of volume. BMI also does not have an adjustment for gender even though healthy women normally carry more body fat than men. For these reasons, doctors combine the BMI with other indicators to determine health risks.