BMI Calculator

Body Mass Index Calculator: this calculator will give you an idea of how your weight compares to height. Body Mass Index (or BMI) is calculated as your weight (in kilograms) divided by the square of your height (in metres) or BMI = Kg/M2.


Imperial   Metric
ft   in


The table below shows the World Health Organization BMI classification system for adults, which is used by Public Health England

The International Classification of adult underweight, overweight and obesity according to BMI
*Adapted from the Public Health England Obesity website

BMI is the most commonly used measure of obesity in adults and used by healthcare professionals to assess future treatment and monitor progress. The ideal BMI for an adult is between 18.5 and 24.9. A measure of above 30 indicates that the patient is obese.

However, BMI is only a guide an approximation to a healthy weight. It is often cited that Jonny Wilkinson in his prime was overweight with a BMI of 27. This, of course ignores the possibility that much of Jonny's weight was actually muscle mass.


Measuring Obesity in Children

BMI is not a reliable indicator of a child's health and is not normally used in its most basic format by the National Child Measurement Programme (NCMP). It is important to consider both age and gender of the child being weighed. Rather than being graded in broad bands the child's measurement is considered in centiles relative to the rest of their peer group.

The following guidance is offered by Public Health England.

  • Clinically Very Underweight: ≤0.4th centile 
  • Clinically Low Weight: ≤2nd centile
  • Clinically Healthy Weight: >2 - <91th centile
  • Clinically Overweight: ≥ 91st centile
  • Clinically Obese*: ≥98th centile
  • Clinically Extremely Obese: ≥99.6th centile

Body Mass Index (BMI) - Limitations and Disclaimer

While BMI is accurate for most people, it doesn't work for everyone and it has limitations. It's important to remember that:

  • If you are under 20 years old or pregnant or breast-feeding, you should not rely on the BMI reading.
  • You could have a high BMI but be at a weight that is considered healthy if you're muscular or athletic.
  • You could have a normal BMI and have poor nutrition.
  • You should not take action based on its values. It's important to talk to your doctor about weight-related health risks.


The BMI calculator is provided for your information only. It is not a substitute for professional medical advice, and may not represent your true individual medical situation. It does not take all possible factors into account in its assessment of your healthy weight. For example, it tends to overestimate body fat in very muscular individuals or in people who are less than 150cm, and may underestimate body fat in people who have lost muscle mass, such as the elderly.