BMI Calculator
Calculate your Body Mass Index from height and weight. Supports both imperial and metric units with instant WHO category classification.
About This Tool
Body Mass Index (BMI) is a simple screening metric that uses your height and weight to estimate whether you fall into an underweight, normal weight, overweight, or obese category. It was developed in the early 19th century by Belgian mathematician Adolphe Quetelet and remains one of the most widely used population-level health indicators today.
The formula is straightforward: divide your weight in kilograms by your height in meters squared (kg/m2). For imperial units, the formula adjusts to (weight in pounds / height in inches squared) * 703. This calculator handles both unit systems automatically -- just toggle between Imperial and Metric using the switch at the top.
The World Health Organization classifies BMI into four primary categories. A BMI below 18.5 is considered underweight, 18.5 to 24.9 is normal weight, 25.0 to 29.9 is overweight, and 30.0 or above is classified as obese. The colored bar below your result provides a visual indication of where your BMI falls on this spectrum.
It is important to understand that BMI has significant limitations. It does not distinguish between muscle mass and fat mass -- a muscular athlete and a sedentary person of the same height and weight will have the same BMI despite very different body compositions. BMI also does not account for bone density, age, sex, ethnicity, or fat distribution. Visceral fat (around organs) is more dangerous than subcutaneous fat, but BMI cannot differentiate between the two.
Because of these limitations, BMI should be used as one data point among many, not as a definitive health assessment. If you have concerns about your weight or health, consult a qualified healthcare provider who can assess body composition, metabolic health, and other relevant factors. This tool is for informational and educational purposes only and does not constitute medical advice.
How to Use
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1
Select your unit system
Toggle between Imperial (lbs, ft/in) and Metric (kg, cm) using the switch.
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2
Enter your weight
Type your weight in pounds (imperial) or kilograms (metric).
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3
Enter your height
For imperial, enter feet and inches separately. For metric, enter your height in centimeters.
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4
View your result
Your BMI, WHO category, and position on the colored scale appear instantly.
Where Does This Data Come From?
BMI is calculated using the standard formula: weight (kg) / height (m)^2. For imperial units, the formula is: (weight (lbs) / height (in)^2) * 703. Categories follow the World Health Organization classification: Underweight < 18.5, Normal 18.5-24.9, Overweight 25.0-29.9, Obese 30.0+. All calculations are performed in your browser -- no data is sent to any server.
