BMI Calculator — CalculatorBox

How to use

Pick your preferred unit system (metric or imperial).
Enter your height and weight.
The calculator updates instantly — BMI and category (underweight / normal / overweight / obese) are shown on the right.

Formula & theory

BMI is defined by the Quetelet index:

metric:    BMI = weight / height²        (kg, m)
imperial:  BMI = 703 × weight / height²  (lb, in)

WHO categories (adults)

Category	BMI range
Underweight	< 18.5
Normal	18.5 – 24.9
Overweight	25 – 29.9
Obese	≥ 30

Limitations

BMI does not distinguish muscle from fat, nor account for body composition, ethnicity, age, or sex. Clinicians often combine BMI with waist circumference or body-fat percentage for a fuller picture.

Frequently asked questions about BMI Calculator

What BMI range is considered healthy?

For most adults a BMI between 18.5 and 24.9 is considered healthy. Under 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese.

Does BMI work for athletes or children?

BMI is a population-level indicator. It can be misleading for muscular individuals, athletes, elderly people, pregnant women, or children — use it only as a rough reference.

Is my data stored?

No. All calculations happen in your browser; nothing is sent to a server.