In short

  • BMI is a height-to-weight screening ratio, not a direct body-fat measurement.
  • Body-fat methods answer a different question and can disagree with one another.
  • Interpret either value with other health information rather than as a diagnosis.

BMI is a height-to-weight ratio

Body mass index divides weight in kilograms by height in meters squared. It is quick, inexpensive and useful for population screening, but it does not directly measure tissue composition.

Body-fat estimates ask a different question

Body-fat percentage aims to estimate how much body mass is fat. Skinfolds, bioelectrical impedance and imaging use different methods and can disagree because hydration, device quality and technique affect the result.

Where BMI can mislead

Two people can have the same BMI with different amounts of muscle and fat. Pregnancy, older age, high muscularity and differences in fat distribution also limit an individual interpretation.

Use more than one signal

BMI can be one screening input alongside waist measurement, blood pressure, laboratory results, medical history and a clinician’s assessment. It is not a diagnosis on its own.

Sources

These primary or official references support the formulas, definitions or scope used in this guide.