What is BMI | Body Mass Index | Ramsay Health Care

0808 278 1276

Talk to one of our dedicated weight loss enquiry handlers

Or Send us a message...

Why We're Different

  • Access to a team of specialist bariatric nurses – expert medical advice and regular medical reviews
  • Access to the hospital out of hours service
  • Access to a dietician - expert nutritional advice on making the most of the procedure you have chosen to have
  • 2 x-ray adjustments and up to 6 clinical adjustments
  • Access to your surgeon as clinically indicated
  • Access to support groups for patients
Find Out More

What is BMI and how does it work?

BMI is an acronym for the term body mass index. It’s a measurement of a person’s body weight in relation to their height for all adults, irrespective of age and sex.

In 1985 the National Institutes of Health (NIH) recommended that physicians adopt the BMI as an index of obesity. It has now become the standard formula to determine what is a healthy weight, underweight, overweight and obese. These weight categories are used to help assess a person’s risk of obesity related diseases.

How does it work for adults?

You need to know your height and weight and input them into the standard BMI formula. BMI is calculated by dividing a person’s weight in kilograms by the square of their height in metres (kg/m2).

Metric BMI formula

BMI = Weight (kg) / Height (m)²

Imperial BMI formula

BMI = [Weight (lbs) / Height (inches)²] x 703

The imperial BMI formula uses a conversion factor of 703.

How does BMI work for children?

For children the relationship between weight classification and BMI varies with age and sex. Children’s BMI measures are usually compared to a growth reference in order to determine a child’s weight status.

Some factors, for example timing of puberty or ethnicity, can make the classification of children’s BMI more complex. There are a number of different child growth references and associated thresholds. In the UK, we most often use the UK90 Growth Reference.

The link between BMI thresholds and future morbidity and mortality is weaker for children than for adults but evidence shows that children with a high BMI are more likely to have a high BMI in adulthood, and therefore a raised risk of future health problems.

How is BMI used?

BMI is a proxy measure of excess body fat. Doctors use BMI as a screening tool to signpost a person’s weight category. A person with a high BMI indicates they may have high body fatness and an overweight or obese weight status with an increased risk of obesity related illnesses. BMI is not a diagnostic tool of an individual’s body fatness or health so further tests are required.

BMI is the most commonly used measure for monitoring the prevalence of overweight and obesity at population level.

How are BMI levels interpreted?

BMI provides an indication of your health status. The BMI categories are:

Underweight = BMI<18.5

Normal weight = BMI 18.5–24.9

Overweight = BMI 25–29.9

Obesity = BMI of 30 or above

Why use BMI?

BMI is an easy and non-invasive method of accurately and consistently assessing excess body fat at a population level. Excess body fat is linked to a person’s current and future morbidity. True measures of BMI are expensive or impractical and other proxy measures are more difficult to measure precisely.

BMI population data has been compiled on a worldwide scale.

Limitations of BMI

BMI has limitations. It may not be an accurate tool for assessing weight status at an individual level as it does not take into account a person’s fitness and muscle mass, their ethnic origin, body shape, age and sex. It also doesn’t provide an indication of body fat distribution.

At a population level these limitations are not seen as particularly important as they even out across large numbers of people.
Are You Eligible

Are You Eligible?

Weight loss surgery is performed to control weight. There are two basic ways that weight loss surgery works to help patients lose weight and improve both physical and lifestyle conditions.

Find Out More

FAQ

Benefits of Surgery

Weight loss will improve the physical and lifestyle conditions associated with being overweight.

Find Out More

How Are We Different

How Are We Different?

We know how hard the fight with obesity is...members of our team have had the surgery themselves and therefore our multidisciplinary team can talk from real life experience about weight loss surgery.

Find Out More

Your Aftercare

Your Aftercare

We invest heavily in resources for our post operative care. Feel safe in the hands of our specialist multi disciplinary team.

Find Out More

Benefits Of Surgery

Frequently Asked Questions

Weight loss surgery is the first part of a long process, aftercare is the key to success. Support is ultimately the one part of the journey that truly does make a real difference.

Find Out More

Weight Loss Prices

Weight Loss Prices

Weight loss surgery is the first part of a long process, aftercare is the key to success. Support is ultimately the one part of the journey that truly does make a real difference.

Find Out More

Weight Loss Blog


Keep up to date with the latest Ramsay Health Care weight loss blogs

Weight Surgery Hero

What are the Different Weight Loss Surgeries?

There are a number of different weight loss surgery options that can produce significant and sustained results, find out which one is best for you.

Continue Reading
Weight Loss Surgery Criteria Hero

Who Qualifies for Weight Loss Surgery?

Weight loss surgery is used as a treatment for patients who are obese & requires a life-long commitment to weight loss - several factors your bariatric surgeon will asses before recommending it

Continue Reading
Healthy Loss Hero

How to Lose Weight Healthily

When deciding to lose weight, it’s important to set yourself realistic and achievable goals, and to go about it in a healthy way.

Continue Reading
avoid-obesity

How to Avoid Obesity

According to statistics from Cancer Research UK, after smoking, obesity is the biggest cause of cancer in the UK. So how do you avoid becoming obese? Here are some tips

Continue Reading

Talk to one of our dedicated weight loss enquiry handlers

Our specialist enquiry handlers will be able to help you with any questions you may have!