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What is BMI?
BMI stands for Body Mass Index. It is a simple measure used to assess whether an adult’s weight is in a healthy range for their height.
In the UK, BMI is commonly used by the NHS as a screening tool. It can help give a general idea of weight status, but it does not tell the full story about a person’s health.
The BMI formula
The formula for BMI is weight in kilograms divided by height in metres squared. In other words, BMI = kg/m².
If you prefer to work it out step by step, first measure your weight in kilograms. Then measure your height in metres, square that number, and divide your weight by the result.
An example calculation
For example, if someone weighs 70 kg and is 1.75 metres tall, the height is squared first. That gives 1.75 × 1.75 = 3.06.
The next step is to divide 70 by 3.06. The BMI would be about 22.9.
BMI categories in the UK
In adults, a BMI below 18.5 is usually considered underweight. A BMI between 18.5 and 24.9 is classed as a healthy weight.
A BMI between 25 and 29.9 is considered overweight. A BMI of 30 or above is classed as obese.
Limitations of BMI
BMI is useful because it is quick and easy to calculate. However, it does not measure body fat directly.
It may be less accurate for people who are very muscular, pregnant, elderly, or from some ethnic backgrounds. It also does not show where fat is carried on the body, which can affect health risks.
How BMI is used
The NHS and other health services may use BMI as one part of a wider health check. It can be helpful for spotting possible weight-related risks.
Still, BMI should be considered alongside other factors such as waist size, diet, activity levels, and medical history. A healthcare professional can help interpret the result properly.
Where to calculate BMI
Many people use a BMI calculator online to save time. These calculators usually ask for your height and weight, then give your BMI automatically.
If you want to calculate it yourself, just remember the formula: weight in kilograms divided by height in metres squared. It is a quick way to get a rough guide to your weight status.
Frequently Asked Questions
BMI is calculated by dividing a person's weight in kilograms by the square of their height in meters.
BMI = weight (kg) / [height (m)]^2.
Yes, the formula is BMI = (weight in pounds / [height in inches]^2) x 703.
Squaring the height adjusts for the two-dimensional nature of body surface area relative to height.
Kilograms for weight and meters for height.
The calculation is the same, but interpretations of BMI values differ for children and adults.
BMI = 70 / (1.75 * 1.75) = 22.86.
BMI stands for Body Mass Index.
Yes, use an online BMI calculator where you input your height and weight.
BMI = weight (kg) / [height (m)]^2.
BMI = (weight in pounds / [height in inches]^2) x 703.
No, the BMI formula is the same for both males and females.
It is a conversion factor to account for the difference in units between metric and imperial systems.
Divide the height in centimeters by 100 to get height in meters.
BMI is used to assess whether a person has a healthy body weight for their height.
Yes, you can calculate it manually using the appropriate formula and your height and weight.
Yes, high muscle mass can result in a high BMI even if a person is not overweight.
The calculation is the same, but the results are interpreted using age- and sex-specific percentiles.
BMI is a useful screening tool but may not accurately represent body fat for all individuals.
You need your weight and your height.
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