Body Mass Index (BMI) Calculator

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Body Mass Index (BMI) is a number calculated from a person’s weight and height. BMI is a reliable indicator of body fatness for people. BMI does not measure body fat directly, but research has shown that BMI correlates to direct measures of body fat and 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. 

How is BMI used?

BMI is used as a screening tool to identify possible weight problems for adults. However, BMI is not a diagnostic tool. For example, a person may have a high BMI. However, to determine if excess weight is a health risk, a healthcare provider would need to perform further assessments. These assessments might include skinfold thickness measurements, evaluations of diet, physical activity, family history, and other appropriate health screenings. 

BMI Calculator

Your BMI (Body Mass Indicator) is an objective scientific measure, that uses your height and weight to determine approximate body fat.

Height (m)
Weight (Kgs)

Click & Drag the Sliders below to calculate your BMI


Someone with a BMI of below 18.5 is considered underweight. Whilst some people are naturally slim, being underweight from poor nutrition, or as a result of other disease, can have serious health risks. Illness associated with being underweight ranges from simple tiredness due to inadequate energy intake, through to reduced immunity to infections, anaemia, vitamin deficiencies, thinning of the bones, infertility and heart rhythm irregularities. If your BMI is under 18.5 you should discuss it with your doctor. They will want to make sure you don’t have any illness causing the weight loss and then will advise you about how to safely gain weight

A BMI of 18.5 to 24.9 suggests a normal healthy weight. This means your body is not at risk of weight-related disease. You still need to ensure a balanced diet with plenty of fresh fruit, vegetables and good vitamin and mineral intake, but if your calorific intake is matching your energy output you will remain a normal weight.

With a BMI of 25 to 29.9 many people may only notice they are overweight when their clothes get tighter - by then the excess weight you're carrying will already have silently started to damage your blood vessels, hormone system and joints, raising your risk of diseases such as:

  • Heart disease
  • High blood pressure
  • Diabetes
  • Arthritis
  • Infertility
  • Asthma
  • Cancer
Although you may feel no different, you need to take action whilst the effects of being overweight can be reversed more easily - you need to gently reduce your calorific intake and increase your activity level. Crash diets don’t work - you need to change your lifestyle. Even slight changes make a difference - two less chocolate biscuits, or one less glass of wine a day can lose you 5lb in fat during the year. Simply parking the car at the far end of the car park or using the stairs instead of the lift will over time make a noticeable difference.

With a BMI of 30 to 35 you're now medically classified as obese - this means you're at high risk of weight related illness, such as:

  • Heart disease
  • Diabetes
  • Arthritis
  • Infertility
  • Miscarriage
  • Asthma
  • Fatty liver disease
  • Cancer
But if you can lose even just a little weight your risk will drop - Just a five per cent weight loss (from 80kg to 76kg) has been shown to significantly reduce the health risks associated with obesity, such as reducing your cholesterol levels and blood pressure and giving you better blood sugar control. To have a BMI over 35 is considered as being very obese and this means that obesity-related illnesses could severely affect the quality of your life and shorten your lifespan by several years. Yet even now it’s not too late to do something about it. Improved fasting insulin and thus glycaemic control in patients with type 2 diabetes, even coming off the medication you may take for diabetes or blood pressure is possible if you can lose some weight. You should see your doctor and talk about getting help. If your BMI has reached 40 or more you're ‘morbidly obese’ - you will be 80 times more likely to develop type two diabetes than someone with a normal BMI, your lifespan will be shortened by over ten years and your quality of life will be reduced in many ways.

Other Health Calculators, such as the Healthy Weight Calculator and the Ideal Hip-Waist Ratio can be used as a comparison with your BMI results and will help you further determine whether your weight should be reduced.

Ideal Hip-Waist Ratio

The Waist-Hip ratio gives an indication of how much fat is stored in the abdomen. This can be used as a very good measure of your relative health. Men and women, of course, have different targets for Waist-Hip ratio. 

Enter waist size (narrowest point):    inches

Enter hip size (widest point) :             inches

Your Waist-Hip Ratio is:

For women: an ideal figure is 0.72 or less. Studies show that women have greatly increased chance of getting coronary disease and related health problems if their Waist-Hip ratio exceeds 0.72. 

For men: an ideal figure is 0.89 or less. Studies show that men have greatly increased chance of getting coronary disease and related health problems if their Waist-Hip ratio exceeds 0.89.