BMI Calculator
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About this tool
Body Mass Index (BMI) is a simple screening number that relates your weight to your height. It is calculated as weight in kilograms divided by height in metres squared, and this calculator supports both metric (cm, kg) and imperial (ft, in, lbs) units, converting for you.
After you enter your height and weight it shows your BMI value and the World Health Organization category it falls into: underweight below 18.5, normal from 18.5 to 24.9, overweight from 25 to 29.9, and obese at 30 or above.
BMI is a quick population-level indicator, not a diagnosis. It does not distinguish muscle from fat, so very muscular people can read high while a normal number can hide other health factors. Use it as one rough signal and speak to a professional about anything that matters.
How to use
- Choose Metric (cm/kg) or Standard (ft/in/lbs) units.
- Enter your height and weight.
- Press Calculate to see your BMI and its category.
- Compare the value against the category ranges shown.
Common use cases
- Getting a quick sense of where your weight sits relative to guidelines
- Tracking a BMI trend over time as part of a fitness plan
- Converting between metric and imperial body measurements
- A starting point for a conversation with a doctor or trainer
Frequently asked questions
How is BMI calculated?
BMI equals weight in kilograms divided by height in metres squared. The tool supports both metric and imperial units.
What do the BMI categories mean?
Per WHO guidelines: under 18.5 is underweight, 18.5–24.9 normal, 25–29.9 overweight and 30 or above obese.
Is BMI accurate for everyone?
BMI is a quick general indicator and ignores muscle mass and body composition, so athletes can read high. Treat it as a rough guide.
Does BMI apply to children or athletes?
Not directly. Children use age- and sex-specific percentiles, and very muscular athletes often read as overweight despite low body fat. Those cases need specialised measures.
Is a normal BMI a clean bill of health?
No. BMI ignores fat distribution, muscle, and many other factors. It is a screening signal, not a diagnosis — other measurements and a professional opinion matter.