body mass index (bmi)

The Body Mass Index (BMI) describes relative weight for height. It is significantly correlated with total body fat content. BMI does not measure body fat directly, but can be considered an alternative for direct measures of body fat. Additionally, BMI is an inexpensive and easy-to-perform method of screening for weight categories that may lead to health problems.

Body Mass Index (BMI) Calculator

Body mass index (BMI) calculation is based on the following formulas:

Kilograms and centimetres:
BMI = weight (kilograms)/[height (centimetres)/100]²

Pounds and inches:
BMI = {weight (pounds)/[height (inches)]²}x703

Interpretation of Body Mass Index (BMI)

For adults Body Mass Index (BMI) is interpreted using standard weight status categories that are the same for all ages and for both men and women.

Classifications for BMI
BMI
Below 18.5	Underweight
18.5 – 24.9	Normal weight
25 – 29.9	Overweight
30 – 34.9	Obesity (Class 1)
35 – 39.9	Obesity (Class 2)
40 or higher	Extreme obesity (Class 3)

Correlation between the BMI number and body fatness is strong, but it is important to remember that BMI is not a direct measure of body fatness. Body Mass Index is calculated from an individual’s weight that includes both muscle and fat. It overestimates apparent body fatness for very muscular adults (body builders), and it underestimates apparent body fatness for adults with very little muscle (elderly).

Body Mass Index for children and teens

BMI number is calculated the same way, but for children and teens, BMI is age and sex specific and is often referred to as BMI for age.