Obesity, explained simply 📚

BMI — body mass index — explained in plain language: how it is calculated, what the numbers mean for adults and children, and a free calculator.

Overweight and obesity are not the same thing. Here are the official definitions for adults and children, the three classes of obesity, and how common each is.

Obesity raises the risk of diabetes, heart disease and other illnesses. What WHO and the World Obesity Federation say, and what the data shows.

Measured or self-reported? Survey or model? How the numbers on this site are produced, and why the same country can have two different obesity figures.

BMI is useful for studying whole populations, but it has real limits for individuals. What BMI can and cannot tell you, according to the CDC.

Six common ideas about obesity, checked against real data from WHO, the UN and the US CDC.

Plain-English meanings of words used in obesity statistics: age-standardized, prevalence, BMI-for-age, uncertainty interval, self-reported and more.