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What is BMI?

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BMI, or Body Mass Index, is a calculation used within healthcare to measure if you are a healthy weight. It takes into account your height and weight to produce a score that sits within various categories.

Your BMI score is not a reflection of your body fat percentage but can help some people to determine if they are over or underweight.

Here we’ll share how to calculate your BMI, what your score means and how else you can measure your health risk.

BMI calculator

Adults can use a BMI calculator to work out their individual score. To calculate your Body Mass Index, you'll need to know your weight in kilograms and your height in metres.

Step one: Multiply your height in metres by itself, eg 1.7 x 1.7= 2.89
Step two: Divide your weight in Kilos by this figure, e.g 80 ÷ 2.89 = 27.7
Step three: For this example 27.7 is your BMI

BMI is interpreted differently in children aged 2 to 18 who are constantly growing. A child’s Body Mass Index score also considers age and sex to deliver a percentile score.

BMI chart

A Body Mass Index chart is a helpful way to visualise how the different scores sit across the various BMI categories. These range from underweight to obese.

BMI table

What does your BMI score mean?

An ideal BMI score for most adults is between 18.5 to 24.9 (healthy weight category). Find your score in the below categories to determine what yours means.

Below 18.5

A score this low means that you may be underweight. This could be due to various reasons including ongoing medical conditions or a loss of appetite.

It’s important to speak to your GP if you are struggling to gain weight or feel anxious when you think about food as you may have an eating disorder.

Having a low BMI score and being underweight can cause various health risks including:

  • Malnourishment and nutritional deficiencies
  • Depression and anxiety
  • Irregular menstrual cycles and fertility issues
  • Low immune system

18.5 – 24.9

For most adults, this range is an ideal BMI score, and it shows that you're at a healthy weight for your height. Continue to stay active, drink plenty of water and eat healthy by consuming a balanced diet to maintain your Body Mass Index.

Being of a healthy weight will help you to have good general health and to decrease your risk of conditions such as:

Being healthy can also help you to sleep better, have more energy, feel more confident and avoid aches and pains.

25 to 29.9

Your BMI is above the ideal range and this score means you may be overweight. This means that you're heavier than is healthy for someone of your height. Carrying excess weight can put you at increased risk of heart disease, stroke and type 2 diabetes.

Find out how you can healthily lose weight to help promote better overall health.

30 or more

A BMI above 30 is considered as obese. Being obese puts you at a raised risk of various health problems such as:

  • Coronary heart disease
  • Stroke
  • Hypertension
  • Diabetes

Losing weight will help to improve your health and well-being. Learn more about how to take care of your heart health.

How accurate is body mass index?

In general, Body Mass Index is a helpful tool to understand if you are a healthy weight for your height. However there may be some limitations.

Whilst BMI considers various body shapes and sizes, it doesn’t account for age, gender or muscle mass.

BMI isn’t able to differentiate between body fat and muscle, which is much denser than fat. This can make bodybuilders, athletes and those with a lot of muscle bulk weigh more than someone else their height, giving them a higher BMI score even though they are healthy.

You also can’t use BMI as a measure of healthiness if you are pregnant. In this instance you should speak to your midwife or GP.

Why is waist size also important?

The circumference of your waist is an important indicator of health and weight, sometimes more so than BMI. This is because BMI doesn’t consider where body fat is distributed.

Carrying fat around your middle can put pressure on your organs and impact the abdominal region. Excess fat around or inside your organs can increase your risk of various obesity-related health conditions such as high blood pressure, diabetes and heart disease.

Below are the categories for waist circumference for men and women of white European, Middle Eastern, black African and mixed origin:

  • Low risk: below 37 inches (94 cm) for men / below 31.5 inches (80cm) for women
  • High risk: 37-40 inches (94-102 cm) for men / 31.5-34.6 inches (80-88cm) for women
  • Very high risk: more than 40 inches (102cm) for men / more than 34.6 inches (88cm) for women

The guidelines are slightly different for men and women of South Asian, Chinese, Japanese or African Caribbean origin. Anything above 31.5 inches (80cm) for women and 35.4 inches (90cm) for men is considered very high risk. There is no ‘high risk’ category and anything below is considered ‘low risk’.

Measuring your waist size is easy to understand and works well for those who are more likely to carry fat around their middle or have a higher muscle mass.

  1. Start by standing tall and find the area between the top of your hip bones and bottom of your ribs.
  2. Wrap a tape measure flat against your body around your waist (just above the belly button). It should be snug to your skin but not too tight.
  3. Exhale and take your measurement.

In summary, BMI is an approximate measure of your body weight compared to your height. Your score may indicate whether or not you are of a healthy weight, however it doesn’t take into account your muscle mass, age or gender. Measuring your waist circumference may provide additional indication of health risk.

Being overweight and underweight can lead to serious health problems, so it’s important to practice healthy eating and stay active. Learn more about weight management at LloydsPharmacy where you can discover more helpful articles such as a guide to the keto diet, fitness trackers and how to accept yourself at every weight.

Weight loss service

References

www.nhs.uk/common-health-questions/lifestyle/what-is-the-body-mass-index-bmi
www.nhs.uk/live-well/healthy-weight/managing-your-weight/advice-for-underweight-adults
www.uhcw.nhs.uk/download/clientfiles/files/Patient%20Information%20Leaflets/Core%20Services/Trust-Wide/117228_MECC_-_Maintaining_a_healthy_weight_(1799)_%5BJan_18%5D.pdf
www.bhf.org.uk/informationsupport/heart-matters-magazine/medical/measuring-your-waist