BMI Calculator
Calculate Body Mass Index
How to use this tool
- Select your unit system (Metric or Imperial)
- Enter your weight in kg or pounds
- Enter your height in cm or feet/inches
- Click Calculate to see your BMI and category
About this tool
BMI (Body Mass Index) is a screening tool that uses height and weight to estimate body fat. It helps categorize individuals into underweight (<18.5), normal (18.5-24.9), overweight (25-29.9), or obese (≥30) categories. Note: BMI doesn't account for muscle mass, bone density, age, gender, or overall body composition. Athletes may have high BMI due to muscle mass. Always consult a healthcare provider for a complete health assessment.
Frequently asked questions
How is BMI calculated?
Weight in kilograms divided by height in metres squared. Someone 1.75 metres tall weighing 70 kilograms has a BMI of 70 divided by 3.0625, which is 22.9. Imperial input is converted to metric first, which is the same as the older formula of pounds divided by inches squared times 703.
What do the BMI categories mean?
Under 18.5 is classed as underweight, 18.5 to 24.9 as normal, 25 to 29.9 as overweight and 30 and above as obese. Those thresholds come from population statistics on health risk, not from a measurement of any individual's health.
Is BMI accurate for everyone?
No, and it was never meant to be. It cannot tell muscle from fat, so athletes and heavily built people routinely register as overweight while carrying very little fat. It also does not account for age, sex, bone density or where fat is distributed, and abdominal fat carries more risk than the same weight elsewhere.
Does BMI work for children?
Not with these thresholds. Children and teenagers are assessed against age and sex specific percentile charts, because normal body composition changes substantially during growth. Use a paediatric BMI-for-age chart instead.
What should I do if my BMI is outside the normal range?
Treat it as one screening number among several, not a diagnosis. Waist measurement, blood pressure, activity level and family history all say more about health risk than BMI alone. A doctor can interpret it in context; a single figure cannot.
Is my height and weight sent anywhere?
No. The calculation runs in your browser and nothing you enter is uploaded, stored or logged.