How BMI is calculated
According to the NHS website, BMI is calculated by dividing an adult’s weight in kilograms by their height in metres squared.
For example, if you weigh 70kg (around 11 stone) and are 1.70m (around 5ft 7in) tall, you work out your BMI by:
1. Squaring your height in metres: 1.70 x 1.70 = 2.89
2. Dividing your weight in kilograms: 70 ÷ 2.89 = 24.22
Your result will be displayed to one decimal place, for example, 24.2.
For most adults, if your BMI is:
Below 18.5 – you’re in the underweight range
18.5 to 24.9 – you’re in the healthy weight range
25 to 29.9 – you’re in the overweight range
30 to 39.9 – you’re in the obese range
40 or above – you’re in the severely obese range
If you have an Asian, Chinese, Middle Eastern, Black African or African-Caribbean family background you’ll need to use a lower BMI score to measure overweight and obesity:
23 to 27.4 – you’re in the overweight range
27.5 or above – you’re in the obese range
What your result means:
A higher BMI increases the chance of developing long-term conditions, such as type 2 diabetes and heart disease.
The BMI calculation is just one measure of health. It cannot tell the difference between muscle and fat.
For example, if you have a lot of muscle, you may be classed as overweight or obese despite having low body fat.
People who are very muscular, like professional sportspeople, can have a high BMI without much fat.
