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Body Mass Index (BMI) Calculator

Body Mass Index (BMI) is the assessment used to indicate how healthy a person’s weight is in relation to their height. You can use the body mass index calculator to find out if you have a healthy BMI.

If you know your height and weight, you can work out which weight range you’re in using the simple steps outlined below.

  1. Take your weight in kilograms (kg) and divide it by your height in metres squared (m²).
  2. Then divide the result by your height in metres (m) again.

For example, if you weigh 70kg, and you’re 1.75m tall, your BMI would be 22.9 (70/1.75 = 40 and 40/1.75 = 22.9).

Alternatively, use our body mass index calculator. Simply enter your height and weight to find out your BMI.

Body Mass Index Calculator

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The BMI weight ranges, as set out by the World Health Organisation (WHO), are outlined below.

  • If your BMI is less than 18.4, you are underweight for your height
  • If your BMI is between 18.5 and 24.9, you are an ideal weight for your height
  • If your BMI is between 25 and 29.9, you are over the ideal weight for your height
  • If your BMI is between 30 and 39.9, you are obese
  • If your BMI is over 40, you are very obese.

If you have a BMI of over 25, you need to think about losing weight because you have an increased risk of developing serious health problems, such as heart disease, diabetes, and several forms of cancer.

If your BMI is over 30, you need to make some immediate changes to your lifestyle in order to lose weight. SMG can provide you with advice about how to lose weight safely, however you should also make an appointment to see your GP.


  1. This is general advice for adults only — it does not apply to children.
  2. When you calculate your Body mass index, remember to take into account your frame size and your build — your BMI may not be accurate. For example, your BMI may not be accurate if you’re a weight-trainer, an athlete, or if you’re pregnant, or breastfeeding.
  3. Your BMI maybe affected if you’re over the age of 60. This is because your bones may begin to weigh significantly less as you get older.
  4. If you have a long-term health condition, talk to your GP before starting any weight-loss programme.
  5. Talk to your GP if you have noticeably lost or gained, weight recently for no known reason.

Your BMI will always be accurate — it just may not be a fair reflection on your weight.