The Body Mass Index (BMI) Calculator allows you to measure your BMI using both the US Units (feet, inches, and pound) and Metric Units (centimeter and kilogram). Following are the formulas to calculate BMI in both units.
BMI Formula 

U.S. Units  703 x weight(lb) / height^{2}(in^{2}) 
Metric Units  weight(kg) / height^{2}(m^{2}) 
Following table shows the weight status for different BMI ranges of adults.
Category 
BMI range  kg/m^{2} 
Thinness (Very Severe)  < 16 
Thinness (Severe)  16  17 
Mild Thinness (Underweight)  17  18.5 
Normal or Healthy Weight  18.5  25 
Overweight  25  30 
Obese Class I (Moderate)  30  35 
Obese Class II (Severe)  35  40 
Obese Class III (Very Severe)  > 40 
Following table shows the weight status for different BMI ranges of children and teens.
Category 
Percentile Range 
Underweight  <5% 
Healthy weight  5%  85% 
At risk of overweight  85%  95% 
Overweight  >95% 