How BMI is calculated

BMI is body weight in kilograms divided by height in metres squared: BMI = kg / m². For example, 70 kg at 1.70 m gives a BMI of about 24.2.

BMI ranges for adults

For adults, BMI is commonly interpreted using these screening ranges. They are a guide, not a diagnosis.

BMIBMI ranges for adults
under 18.5Underweight
18.5–24.9Usual BMI range
25.0–29.9Overweight
30.0–34.9Obesity class I
35.0–39.9Obesity class II
40+Obesity class III

When BMI is not enough

BMI does not distinguish fat mass from muscle mass and does not describe fat distribution. Waist circumference, medical history, medicines and overall clinical status can also matter. Adult BMI ranges are not used in the same way for children, adolescents or pregnancy.

What to do with the result

Use the result as a starting point. If your weight, a rapid weight change or related health problems concern you, discuss them with a clinician. Obesity treatment is never decided from one BMI number alone.

Related topics

Weight-loss medications: what options exist in EuropeMedicines used for overweight and obesity are selected according to the approved indication, a person’s health and local availability. They include injections as well as other formulations.→
Weight-loss injections: what they are and when they are usedThe phrase “weight-loss injections” usually refers to prescription medicines used in obesity care. They are not over-the-counter products and they are not suitable for everyone.→
Obesity treatment and medication guides for EuropeChoose the topic that matches what you are trying to understand. Each guide separates general information from the individual decision that belongs to a clinician.→

Sources and review

BMI thresholds and limitations are based on public health guidance. BMI is a screening measure and does not replace clinical assessment.

WHO: Obesity and overweight ↗NHS: BMI calculator for adults ↗

2026-09-12