BMI Calculator

Calculate your Body Mass Index using metric or imperial units. Results follow WHO and CDC adult categories for ages 20 and up. BMI is a screening tool—not a diagnosis.

Disclaimer: This calculator is for informational purposes only and is not medical advice. Consult a qualified healthcare provider for personal health decisions.

Enter weight in kilograms

Enter height in meters (e.g., 1.75)

What BMI means

Body Mass Index relates weight to height. It is widely used as a first-step screen for weight-related health risks but does not measure body fat directly. High or low values may warrant further assessment with a healthcare provider.

Adult BMI categories (WHO/CDC)

Underweight: below 18.5

Normal: 18.5–24.9

Overweight: 25.0–29.9

Obese: 30.0 and above

Read our BMI calculator guide for a longer explanation. Sources: WHO · CDC

How This Calculator Works

1

Enter height and weight

Choose metric or imperial units and fill in both fields.

2

Apply the BMI formula

Weight is divided by height squared (× 703 for imperial).

3

See your category

Your number is mapped to standard adult underweight, normal, overweight, or obese ranges.

About BMI Calculator

Enter height and weight to compute BMI and see a standard adult category. Calculations run in your browser—nothing is stored on our servers. For children, athletes, older adults, or clinical decisions, interpret results with a qualified provider.

Screening only

BMI flags possible risk—it does not diagnose disease on its own.

Muscle vs fat

Very muscular people may score high despite low body fat.

Adults 20+

Pediatric BMI uses age- and sex-specific percentiles, not these cutoffs.

How to Use This Tool

1

Choose units

Select metric (kg, m) or imperial (lb, in).

2

Enter weight

Input your current weight in the selected unit system.

3

Enter height

Input your height in meters or inches.

4

Calculate

View your BMI value and WHO/CDC category instantly.

5

Discuss with a provider

Use the result as a starting point for health conversations, not as a diagnosis.

Pro Tips

  • BMI is for adults 20+; use pediatric charts for children
  • Athletes may have high BMI from muscle—consider body composition if relevant
  • Waist circumference can help assess abdominal fat when BMI is borderline
  • Track trends over time rather than reacting to a single reading
  • Consult a healthcare provider for personalized advice

Frequently Asked Questions

How is BMI calculated?
Metric: BMI = weight (kg) ÷ height (m)². Imperial: BMI = weight (lb) ÷ height (in)² × 703. This calculator applies the standard formula and maps your result to WHO/CDC adult categories.
Why does BMI not distinguish between muscle and fat?
BMI uses total body weight relative to height. It cannot tell muscle from fat, so athletes or very muscular people may have a high BMI despite low body fat. Body composition tests or waist measurements can add context.
Is this calculator for children and teens?
No. The same formula applies, but children's BMI must be interpreted using age- and sex-specific percentiles. This tool uses adult cutoffs for people 20 and older. Use CDC BMI-for-age charts for pediatric assessment.
What are the adult BMI categories?
Underweight: below 18.5. Normal: 18.5–24.9. Overweight: 25.0–29.9. Obese: 30.0 and above. Class II obesity is 35.0–39.9; Class III (severe) is 40.0 and above.
How does waist circumference relate to BMI?
For adults with BMI between 25 and 34.9, providers often measure waist circumference to assess abdominal fat. Rough guidance: increased risk is often cited above 40 inches (men) or 35 inches (women)—confirm with your clinician.
Can BMI diagnose a medical condition?
No. BMI is a screening tool only. Diagnosis requires a full clinical evaluation including history, exam, and sometimes lab work or other measurements.

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