The Body Mass Index - its use, meaning and limitations

The Body Mass Index (BMI) has become an established and widely recognised method of helping determine whether someone is a healthy weight when their weight is compared against their height.

If you know your height and weight you can calculate your BMI using our online BMI Calculator.

BMI ranges and their meaning

There are 5 main 'zones' or 'ranges' that your BMI can fall into. These zones have been defined by the World Health Organisation and are as follows:

A BMI of less than 18.4 indicates that you may be underweight for your height you should contact your health professional with a view to discussing how to put weight on.

A BMI of between 18.5 and 24.9 means that you are an ideal weight for your height and you should maintain a healthy diet to keep your BMI in this zone.

A BMI between 25 and 29.9 indicates that you are probably overweight for your height and should try and eat a well balanced healthy diet and exercise more.

If your BMI is between 30 and 39.9 then you are obese. You should contact your GP or health professional to discuss how to lose weight.

If your BMI is 40 or above then you are severely obese. You should contact your GP or health professional to discuss how to lose weight.

BMI Limitations

Not all people should use the BMI as an indication of whether they are a healthy weight. The BMI should be used by healthy adults. The BMI may be affected and inaccurate in the following groups:

  • Children and young adults
  • Adults over 60 years (due in part to bone weight reducing)
  • Adults with a high level of muscle tissue (e.g. athletes / body builders etc) who may fall into the overweight range when in fact they are a healthy weight.
  • Pregnant women or women who are breastfeeding

Calculate your BMI