Your BMI
BMI Chart — WHO Weight Categories
| BMI range | Category | What it means |
|---|---|---|
| Below 18.5 | Underweight | Weight may be too low for your height; consider a check-up |
| 18.5 – 24.9 | Normal weight | Healthy range for most adults — maintain it |
| 25.0 – 29.9 | Overweight | Slightly above the healthy range; small changes help |
| 30.0 and above | Obese | Higher health risk; medical guidance is recommended |
How to Calculate Your BMI
Choose metric (kilograms and centimeters) or imperial (pounds, feet and inches) — the calculator converts everything for you.
Type your measurements. The BMI value, category and healthy weight range update live as you type — no button to press.
The color gauge shows where you sit on the WHO scale, and BMI Prime tells you how close you are to the healthy limit of 25.
What Is Body Mass Index?
Body mass index (BMI) is the most widely used screening measure for body weight relative to height. It was devised in the 1830s by the Belgian statistician Adolphe Quetelet and is calculated by dividing your weight in kilograms by the square of your height in meters (kg/m²). If you use pounds and inches, the formula becomes 703 × lb / in² — exactly what this calculator applies when you switch to imperial units.
The World Health Organization groups adult BMI into four main categories: underweight (below 18.5), normal weight (18.5–24.9), overweight (25–29.9) and obese (30 and above). Large population studies link BMI values outside the normal range to higher risks of cardiovascular disease, type 2 diabetes, joint problems and some cancers — which is why BMI remains the first number doctors look at during routine check-ups.
That said, BMI is a screening tool, not a diagnosis. It cannot distinguish muscle from fat: a muscular athlete may register as "overweight" while carrying very little body fat, and an older adult can have a "normal" BMI with low muscle mass. For a fuller picture, pair BMI with waist circumference (a marker of abdominal fat), body-fat percentage, and how you actually feel and perform. Any health decision should involve a qualified professional.
This calculator also shows two bonus metrics. BMI Prime is your BMI divided by 25 — values under 1.0 mean you are at or below the healthy upper limit, making progress easy to track. The Ponderal Index (kg/m³) scales better for very tall or very short people, where classic BMI tends to over- or under-estimate. Everything runs locally in your browser: your height and weight are never transmitted, stored or shared.
BMI Calculator — FAQ
How do I calculate my BMI?
BMI = weight in kilograms divided by height in meters squared (kg/m²). With imperial units: BMI = 703 × weight in pounds ÷ (height in inches)². This tool computes it instantly for both systems.
What is a healthy BMI?
For most adults a healthy BMI is 18.5–24.9 (WHO). Below 18.5 is underweight, 25–29.9 is overweight, and 30+ is classed as obese. The healthy weight range shown above is derived from these thresholds and your height.
Is BMI accurate for everyone?
No measure is perfect. BMI doesn't separate muscle from fat, so muscular people can score "overweight" while lean. It's a screening tool — combine it with waist circumference and professional advice for real conclusions.
Does this calculator work for children?
It uses the adult WHO classification (18+). Children and teens need age- and sex-specific BMI percentiles, so use a dedicated pediatric percentile calculator for ages 2–17.
Is my data uploaded anywhere?
No. All calculations run locally in your browser with JavaScript. Your height and weight never leave your device.
What is BMI Prime?
BMI Prime = your BMI ÷ 25 (the upper healthy limit). Under 1.0 means you're within or below the healthy range; above 1.0 shows how far over it you are — e.g. 1.10 means 10% above.