Body Mass Index Calculator
Calculate your Body Mass Index from height and weight, with your healthy-weight range and BMI category.
About the Body Mass Index Calculator
Body Mass Index, or BMI, is a simple screening measure that relates your weight to your height to give a single number used worldwide to flag whether someone is underweight, in a healthy range, overweight, or obese. This Body Mass Index calculator computes it from your height and weight in either metric or imperial units and places the result on the standard category scale.
The appeal of BMI is its simplicity and consistency: it is quick, free, requires no equipment, and lets results be compared across populations, which is why health services and researchers rely on it as a first-pass indicator. The calculator also shows the healthy-weight range for your height, so you can see not just your current category but the weight band that would place you in the healthy zone.
It is worth knowing BMI’s limits. Because it uses only height and weight, it cannot distinguish muscle from fat, so very muscular people can read as "overweight" despite low body fat, and it is interpreted differently for children and across some ethnic groups. Treat BMI as a useful starting signal, not a diagnosis, and discuss anything concerning with a healthcare professional. Your figures stay private in your browser.
Looking for more options? Open the full BMI Calculator — it’s the same tool with every feature.
Frequently Asked Questions
How is Body Mass Index calculated?
BMI is your weight in kilograms divided by the square of your height in metres (kg/m²). In imperial units it is weight in pounds divided by height in inches squared, multiplied by 703. This calculator applies the correct formula for whichever units you choose.
What is a healthy BMI range?
For most adults, a BMI between 18.5 and 24.9 is classed as a healthy weight; below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obese. The calculator shows your category and the healthy weight range for your height.
Is BMI accurate for everyone?
BMI is a useful general screening tool but not a complete measure of health. It does not distinguish muscle from fat, so athletes may read high, and it is interpreted differently for children, older adults and some ethnic groups. Use it as a starting point and consult a professional for a fuller assessment.
Understanding Body Mass Index
How BMI is calculated and categorised
BMI divides your weight by the square of your height (kg/m²), producing a single number placed on a standard scale: under 18.5 is underweight, 18.5–24.9 healthy, 25–29.9 overweight, and 30 or above obese. The same formula and bands are used worldwide, which is exactly what makes BMI useful for comparing across people and tracking your own trend over time without specialist equipment.
What BMI does and does not measure
BMI measures weight relative to height — nothing more. It cannot tell muscle from fat or show where fat is stored, both of which matter for health. A muscular athlete may register as "overweight" despite low body fat, while someone in the healthy range can still carry excess abdominal fat. That is why clinicians pair BMI with measures like waist circumference rather than relying on it alone.
BMI for children and different groups
For children and teenagers, BMI is interpreted using age- and sex-specific percentile charts rather than the fixed adult bands, because healthy body composition changes as they grow. Interpretation can also differ across ethnic groups and for older adults. Treat the adult categories as a general guide, use the child mode where appropriate, and discuss any concern with a healthcare professional who can see the fuller picture.