BMI Calculator: Body Mass Index Explained
Calculate your Body Mass Index and understand healthy weight ranges — with limitations and alternatives.
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BMI Calculator: Body Mass Index Explained Body Mass Index (BMI) is your weight in kilograms divided by the square of your height in meters. A result between 18.5 and 24.9 is classified as healthy weight for adults according to the WHO. The calculation takes under 10 seconds with a BMI calculator, but understanding what the number means — and where it falls short — takes a bit more context. --- See our complete guide to health calculators for the full toolkit. What Is BMI and Where Did It Come From? The BMI formula was invented by Belgian polymath Adolphe Quetelet in the 1830s. He was studying the average properties of the human body in a Belgian population — not individual health risk. For about a century the formula was called the Quetelet Index. Ancel Keys renamed it "Body Mass Index"…
Frequently Asked Questions
What is BMI?
Body Mass Index is a number calculated from height and weight that gives a rough indication of whether a person is underweight, at a healthy weight, overweight, or obese. It was developed in the 1830s by Belgian statistician Adolphe Quetelet as a population-level screening tool.
How do I calculate BMI?
Divide your weight in kilograms by the square of your height in meters: BMI = kg/m². For imperial units, use: BMI = (weight in pounds × 703) / (height in inches²). A 5'9" person weighing 160 lb has a BMI of 23.6.
What is a healthy BMI range?
The WHO defines a healthy adult BMI as 18.5 to 24.9. Below 18.5 is underweight; 25 to 29.9 is overweight; 30 and above is obese. These cutoffs are population averages from large epidemiological studies and are the same globally, though some health bodies adjust them for Asian populations.
What are the limitations of BMI?
BMI does not distinguish between fat mass and muscle mass, so athletes and muscular individuals are often classified as overweight. It also does not account for fat distribution — abdominal fat carries higher health risks than fat in other areas. Age and sex also influence how BMI relates to actual health outcomes.
Is BMI the same for men and women?
The BMI formula is the same, but women naturally carry more body fat than men at the same BMI. A BMI of 25 corresponds to about 28–32% body fat in women but only 20–25% in men. Some researchers argue for sex-specific BMI thresholds, though the WHO has not adopted them.
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