Body mass index (BMI) is used as a measure of body weight category, such as overweight, obese, or underweight. It is the person’s weight in kilograms (kg) divided by the square of height in meters (Formula: weight (kg) / [height (m)]2). The BMI calculators below do this calculation for you, all you have to do is enter the height and weight.

BMI is considered to be a screening tool, not diagnostic tool. There are other methods for measuring body fat that include skinfold thickness measurements (with calipers), underwater weighing, bioelectrical impedance, dual-energy x-ray absorptiometry (DXA), and isotope dilution (1). 

The BMI categories are:

 Underweight < or = 18.5 
 Normal Weight 18.5 – 24.9 
 Overweight 25.0 -29.9 
 Obese > or = 30 

 BMI is measured slightly differently in children and teens compared to adults. For children and teens, gender and age are taken into account. BMI Calculators for both children and adults are included below.


  1. Centers for Disease Control and Prevention (CDC). 2017. Healthy Weight: About Adult BMI. Retrieved from