Body Mass Index Overview

Body Mass Index (BMI) measures a persons weight relative to their height and helps to assess whether a person is underweight, of normal weight, overweight or obese.

BMI is based on a formula which was developed by Belgium statistician Adolphe Quelet.

The formula is designed for adults over 20 years old. Once calculated, a persons Body Mass Index value can be compared to weight status categories to determine if an individual is:

  • underweight (BMI: below 19.5)
  • normal weight (BMI:18.5 - 24.9)
  • overweight (BMI: 25.0 to 29.9)
  • obese (BMI: 30.0 & above)

Whilst health organizations may use different weight status categories the weight status categories on this site are in keeping with the US Centers for Disease Control & Prevention guidelines.

Calculate Body Mass Index

Limitations of Body Mass Index

An individuals Body Mass Index and their corresponding 'weight status' category needs to be placed in context.

Body Mass Index Can:

Overestimate Body Fat
Individuals who are athletic and/or have a muscular build may be categorized as overweight. Body builders are often categorized as obese - however body building may promote a longer life expectancy.
Underestimate Body Fat
Body fat can be underestimated in individuals who have lost muscle mass - this often occurs with older people.

Diseases Associated with Obesity

In general, the greater the BMI the greater the risk of contracting diseases associated with obesity. These diseases include:

  • High Blood Pressure - which can lead to heart failure, stroke, kidney damage and/or loss of vision due to retinal damage.
  • Diabetes - a metabolic disease caused by lack of insulin
  • Arteriosclerosis - narrowing & thickening of the arteries which can cause cerebrovascular and coronary disorders.
  • Hyperlipemia - a high level of fat in the blood which is associated with high cholesterol levels.

Other Risk Factors

Body Mass Index is not a diagnostic tool, it is an indicator of weight status. The risk factors below should also be considered when assessing general health risks.

  • Family History of premature heart disease
  • High Blood Pressure(hypertension)
  • High LDL-cholesterol
  • HDL-Cholesterol
  • Triglycerides
  • High Blood Glucose (sugar)
  • Physical inactivity
  • Cigarette/Tobacco Smoking