What is BMI? Body Mass Index explained

Body Mass Index (BMI) is a simple ratio of weight to height: weight divided by height squared, usually in kilograms per meter squared (kg/m²). Health organizations use it as a general screening number for adults - not a full health assessment.

Adult categories commonly follow World Health Organization (WHO) ranges, from severe thinness through normal, overweight, and obesity classes. The same BMI number can mean different things for people with different muscle mass, age, sex, or ethnicity.

Why people use BMI

• Fast to calculate with only height and weight
• Widely documented ranges for adult populations
• Useful as one input among others - not a standalone diagnosis

What BMI is not

BMI does not measure body fat percentage, fitness, or disease. Athletes and people with high muscle mass can land in “overweight” or “obese” bands without excess fat. Pregnancy and some medical conditions also change how weight should be read.

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