BMI Calculator
Work out your body mass index in seconds, in metric or imperial units. For adults aged 18 and over.
Enter your weight and height to see your BMI. This calculator is for adults aged 18 and over.
What BMI can and can't tell you
BMI (body mass index) is your weight in kilograms divided by your height in metres squared. It is a quick, free screening measure that works reasonably well across whole populations: on average, higher BMI values are associated with a higher likelihood of weight-related health conditions.
What BMI cannot do is describe you as an individual. It is one number built from two measurements, and it knows nothing about your body composition, fitness, waist measurement, blood pressure, family history or anything else that actually determines health. Two people with identical BMIs can be in very different shape.
When BMI is misleading
- Athletes and very muscular people. Muscle weighs more than fat, so a rugby player can register as ‘overweight’ while carrying very little body fat.
- Pregnancy. BMI categories are not designed for pregnancy — weight gain in pregnancy is assessed differently by your midwife or GP.
- Under-18s. This calculator is for adults only. Children and teenagers are assessed using age- and sex-adjusted centile charts, which a GP or public health nurse can do.
- Older adults and some ethnic groups. Body composition changes with age, and health risk can occur at lower BMI thresholds in some ethnic groups — another reason the bands are a starting point, not a verdict.
If your BMI concerns you
A number on a screen is a reason to ask a question, not a judgement. If your BMI concerns you — in either direction — a GP can help you understand what it means in the context of your own health and talk you through your options. Learn about weight-related GP consultations.
This calculator provides general information only and is not a medical assessment, diagnosis or treatment recommendation. WHO adult BMI classification is used. For emergencies call 999 or 112.