HealthGood

Body Metrics

BMI Calculator

Estimate your Body Mass Index — a simple screening tool that compares your weight to your height. BMI works at the population level; pair it with waist measurements and body fat estimates for a fuller picture.

BMI Calculator

What your result means

BMI is grouped into WHO categories: underweight (under 18.5), healthy weight (18.5–24.9), overweight (25–29.9), and obesity (30+).

These thresholds describe statistical risk across populations. Athletes, older adults, and people from certain ethnic backgrounds may sit outside their expected category for healthy reasons.

How we calculate this

We use the WHO formula: weight in kilograms divided by height in metres squared (kg / m²). Imperial inputs are converted before the calculation.

The classification thresholds are the WHO adult cut-offs.

Limitations

BMI doesn't distinguish muscle from fat, ignores fat distribution, and is less accurate for athletes, pregnant women, older adults, and children. It is a screening tool, not a diagnostic one.

When to talk to a professional

If your BMI is below 18.5 or above 30, or if you have other risk factors like high blood pressure or diabetes, talk to your GP or a registered dietitian about a personalised plan.

Frequently asked questions

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Waist-to-Hip Ratio Calculator

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Related guides

References

  1. World Health Organization. https://www.who.int
  2. NHS — Health A to Z. https://www.nhs.uk
  3. Centers for Disease Control and Prevention. https://www.cdc.gov

Browse all calculators or read our evidence-based guides.