How to use this tool

1. Fill in the inputs.
2. Read the result.
3. Copy or download as needed.

About the BMI Calculator

Body Mass Index (BMI) is a simple screening measurement that relates a person's weight to their height, and it is one of the most widely used general health indicators in the world. This calculator supports both metric units (centimeters and kilograms) and imperial units (inches and pounds), so you can use whichever system you are more comfortable with, and it instantly shows your BMI value along with the standard weight category it falls into.

BMI is a screening tool rather than a diagnostic one — it does not directly measure body fat percentage, and it does not account for muscle mass, bone density, age, or sex. It is best used as a quick, general reference point, and any health decisions should involve a qualified professional.

The metric formula divides weight in kilograms by the square of height in meters (BMI = kg / m²). When imperial units are selected, the tool first converts inches to meters and pounds to kilograms behind the scenes, then applies the same formula, so the result is identical regardless of which unit system you use.

The result is then compared against the World Health Organization's standard adult BMI categories: under 18.5 is classified as underweight, 18.5 to 24.9 as a normal weight range, 25 to 29.9 as overweight, and 30 and above as obese. These thresholds are designed for the general adult population and are not adjusted for athletes, older adults, pregnant women, or children, all of whom may need a different assessment method.

Common use cases

• Quick personal health tracking between doctor visits.
• Fitness and nutrition planning as one input among several (alongside body composition, waist measurement, and activity level).
• Educational purposes, such as understanding how BMI is calculated and what its categories mean.
• Insurance or wellness program forms that ask for a BMI figure.
• Comparing BMI trends over time as part of a broader weight management plan.

Tips and best practices

• BMI does not distinguish between muscle and fat, so very muscular individuals may show a higher BMI despite having low body fat.
• For children and teenagers, BMI is interpreted differently using age- and sex-specific percentile charts rather than the fixed adult categories used here.
• Track BMI alongside other markers such as waist circumference and how your clothes fit, rather than relying on it as the sole measure of health.
• If your BMI falls outside the "normal" range, treat it as a prompt to speak with a healthcare provider rather than as a diagnosis in itself.

Frequently asked questions