BMI Calculator
Body Mass Index from weight and height, with category.
Body Mass Index is a quick way to gauge whether your weight sits in a healthy range for your height. Enter your weight and height to get your BMI and its category — a screening guide, not a diagnosis.
Formula / method
Examples
23.4 — Normal
29.4 — Overweight
What BMI actually measures
Body Mass Index is your weight in kilograms divided by the square of your height in metres. It is a quick screening number that sorts most adults into underweight, normal, overweight and obese bands, and it correlates reasonably well with body-fat levels across a population.
BMI is widely used because it needs only two easy measurements and no equipment, which is why doctors and health surveys reach for it as a first-pass indicator.
The standard categories
For adults, the World Health Organization bands are: below 18.5 underweight, 18.5 to 24.9 normal, 25 to 29.9 overweight, and 30 or above obese. This tool shows both your BMI and the band it falls into as you type.
Where BMI falls short
BMI does not distinguish muscle from fat, so very muscular people can read as "overweight" while carrying little fat. It also ignores age, sex and where fat is stored, and it is not designed for children, pregnancy or athletes. Treat it as a starting point for a conversation with a professional, not a diagnosis. For a fat-focused estimate, the Body Fat Calculator uses body measurements instead.
Where it's used
- A quick home screening of weight status as underweight, normal, or overweight
- Doctors and nurses using it as a fast population-level health indicator
- Tracking progress alongside a diet or fitness program over months
- Filling in gym-membership or insurance health questionnaires
- Estimating weight categories (while noting BMI ignores muscle and build)
Real-world examples
- A person 1.75 m tall weighing 70 kg finding their BMI is about 22.9, in the normal range
- Converting a 5'10", 190 lb build to a BMI of about 27.3, in the overweight range
- Someone tracking their BMI falling from 31 to 27 after losing 12 kg over six months
A bit of history
The underlying formula was devised between about 1830 and 1850 by Belgian mathematician and astronomer Adolphe Quetelet as the 'Quetelet Index'; the modern name 'body mass index' was coined much later by American physiologist Ancel Keys in a 1972 paper in the Journal of Chronic Diseases.
Did you know?
Quetelet was a statistician studying the 'average man', not a doctor, and never intended his index to gauge an individual person's health, which is one reason BMI has well-known limits for muscular or athletic bodies.
FAQ
Is BMI accurate for everyone?
BMI is a quick screening number and does not account for muscle mass or body composition. Treat it as a rough guide, not a diagnosis.