BMI calculator
Work out your body mass index and check whether your weight is within the healthy range for your height.
BMI calculator: what it is and how it works
Body mass index (BMI) relates weight to height and is the indicator the World Health Organization uses to classify adults’ nutritional status. It is calculated by dividing weight in kilograms by height in metres squared.
According to the WHO, a BMI below 18.5 indicates underweight; 18.5 to 24.9 is a healthy weight; 25 to 29.9 is overweight; and 30 or above is obesity, divided into three classes. It is a quick reference, but it ignores body composition: a very muscular person can have a high BMI without excess fat. For a fuller picture, you can also calculate your body fat percentage.
How to use it
- Enter your weight in kilograms.
- Enter your height in centimetres.
- See your BMI, your category and your healthy weight range.
BMI = weight (kg) ÷ height (m)²Worked example
Someone weighing 70 kg and 1.75 m tall has a BMI of 70 ÷ 1.75² = 22.9, a healthy weight. For that height, the healthy range is 56.7 to 76.3 kg.
Frequently asked questions
What is a healthy BMI?
For adults, 18.5 to 24.9 is considered a healthy weight. There is no single ideal value within that range.
Does BMI work for children?
Not directly. For children and teenagers, BMI percentiles by age and sex are used.
Why can BMI be misleading?
It does not distinguish muscle from fat or consider where fat is stored. Athletes and older people can be misclassified.
What if my BMI is outside the healthy range?
Treat it as a prompt to talk to your doctor or a dietitian, who will assess your case with other measurements.