BMI Calculator

Use our simple BMI Calculator below to measure your own Body Mass Index.

The Body Mass Index (BMI) is a formula for measuring body fat in adults based on your height and weight. Read more information on Body Mass Index

Please select weight and height above and click calculate

Body Mass Index

The Body Mass Index serves as a way to measure a person's body fat based on height and weight. Your BMI can be used to indicate if you're underweight, normal, overweight or obese.

The BMI is defined as an individual's body weight divided by the square of their height.

Interpreting the Body Mass Index

The World Health Organization regard a BMI of less than 18.5 as underweight which may indicate malnutrition, an eating disorder or other health issues.

A BMI above 25 is considered overweight and above 30 is considered obese.

BMI Value BMI Classification
Under 16.0 Severely underweight
16.0 to 18.5 Underweight
18.5 to 25 Normal
25 to 30 Overweight
30 to 35 Obese Class 1
35 to 40 Obese Class 2
Over 40 Obese Class 3

Limitations of the Body Mass Index

Whilst not an infallible measurement the BMI is a reliable indicator of body mass for the average person and is widely used in medicine.

The main problems with the BMI is that it does not take into consideration factors such as a person's frame-size or muscularity (meaning athletes could be classed as "obese" despite having little bodyfat).

For these reasons, BMI calculations may be inaccurate for such people as athletes, children, the elderly, and the infirm.

Calculating body composition for athletic individuals is more accurately derived using measures of body fat from such techniques as skinfold measurements or underwater weighing.


The Fitstream BMI Calculator is intended for informational purposes only, and should not be interpreted as specific medical advice. A qualified health care provider should be consulted before making decisions about therapies and / or health and fitness conditions.