How BMI is calculated
Body mass index is your weight in kilograms divided by your height in metres squared: BMI = kg / m². In pounds and inches it is 703 × lb / in².
BMI categories for adults (WHO)
- Below 18.5: underweight
- 18.5 to 24.9: healthy weight
- 25.0 to 29.9: overweight
- 30.0 and above: obesity
Some health bodies use lower cut-offs for people of South Asian, Chinese, Middle Eastern, Black African or African-Caribbean background.
What BMI does not tell you
BMI is a quick screening number for populations. It does not measure body fat, muscle or where fat is stored, so very muscular people can show as overweight, and older adults can look healthy while carrying less muscle. Waist size is a useful second check.
This calculator is for adults aged 18 and over. Children and teenagers need age-specific BMI charts, and BMI is not used in pregnancy.
