How to use the BMI Calculator
Enter the information requested in the calculator and select Calculate. The result updates immediately. Review the units and assumptions before using the estimate for an important decision.
- Use consistent units for every value.
- Enter realistic figures rather than rounded guesses where possible.
- Compare the result with the explanation and verify sensitive decisions independently.
BMI Calculator formula
Body mass index divides weight in kilograms by height in metres squared.
Practical example
A person weighing 70 kg at 175 cm has a BMI of about 22.9.
Understanding BMI
Body mass index (BMI) compares weight with height and is widely used as a population-level screening measure. It does not directly measure body fat, muscle mass, bone density, nutrition status or overall health.
BMI formulas
Metric: BMI = weight in kilograms ÷ height in metres².
US units: BMI = 703 × weight in pounds ÷ height in inches².
Adult BMI ranges
- Below 18.5: underweight range.
- 18.5–24.9: healthy-weight range.
- 25.0–29.9: overweight range.
- 30.0 and above: obesity range.
These are general adult screening categories. Health interpretation varies with age, pregnancy, ethnicity, muscularity and medical context. For children and teenagers, clinicians use age- and sex-specific BMI percentiles.
BMI and anorexia nervosa
A low BMI can be one physical sign associated with inadequate nutrition, but anorexia nervosa is a mental health and eating disorder diagnosis that cannot be made from BMI alone. Assessment can include eating behavior, weight history, physical examination, laboratory testing and psychological evaluation.
Some clinical descriptions reference BMI below 17.5 as a low-weight indicator, with lower ranges associated with increasing medical concern. These thresholds are not a self-diagnosis tool. A person can have a serious eating disorder at any body size.
When to seek help
Prompt professional advice is appropriate for rapid or unexplained weight loss, fainting, chest symptoms, severe weakness, dehydration, food restriction, purging, obsessive weight-control behavior or distress about eating and body image. Emergency symptoms require local emergency care.
Limitations
BMI may classify highly muscular people inaccurately and does not show fat distribution. Use the result with other measurements and professional context rather than as a standalone judgment.
Related concepts and terms
body mass index · BMI formula · weight status · healthy BMI range · underweight · body weight · height · BMI screening · anorexia nervosa · eating disorder · clinical assessment · BMI percentile
Questions people ask
How to calculate BMI?
Divide weight in kilograms by height in metres squared. For US units, multiply pounds by 703, then divide by height in inches squared.
How to calculate BMI of the body?
Use measured weight and height in the BMI formula. BMI is a screening measure and does not directly measure body fat.
What is a healthy BMI?
For most adults, the general healthy-weight screening range is 18.5 to 24.9. Individual interpretation can differ.
Does BMI diagnose an eating disorder?
No. BMI alone cannot diagnose or exclude an eating disorder. A qualified professional considers physical, behavioral and psychological information.
Are my values saved?
No. The calculation runs locally in your browser and the values are not submitted.