How to calculate BMI
- Choose metric (centimetres and kilograms) or imperial (feet, inches and pounds).
- Enter your height and weight.
- Click Calculate BMI.
- See your BMI, its category highlighted in the table, and the healthy weight range for your height.
What BMI means
Body mass index is your weight in kilograms divided by your height in metres squared. For someone 170 cm tall weighing 65 kg, BMI is 65 ÷ 1.70² = 22.5. Imperial measurements are converted exactly before calculating. The World Health Organization groups adult BMI into ranges: below 18.5 is underweight, 18.5–24.9 is a healthy weight, 25–29.9 is overweight, and 30 or above is obesity, divided into classes I, II and III.
BMI is a screening measure, not a diagnosis. It doesn’t distinguish muscle from fat or show where fat is stored, so very muscular people may have a high BMI while being healthy. It is not designed for children and teenagers, who need age- and sex-specific charts, or for pregnancy. Some health organisations use lower thresholds for people of South Asian, Chinese and other Asian heritage. For advice about your health, talk to a doctor or healthcare professional.
Using your result
- As a quick, general indicator alongside other measures such as waist size.
- To track changes over time with the same method.
- As a starting point for a conversation with a healthcare professional.
BMI calculator FAQ
Is BMI accurate for athletes?
Often not. Muscle is dense, so athletes can have a high BMI with low body fat.
Can I use this for children?
No. Children’s BMI must be compared with growth charts for their age and sex. Ask a paediatrician or use an official child BMI tool.
Is my data saved?
No. Your height and weight are only used in your browser to calculate the result.