BMI Calculator

1. Select your preferred unit system (Metric or Imperial).
2. Enter your weight in kilograms or pounds.
3. Enter your height in centimeters (Metric) or feet and inches (Imperial).
4. Your BMI, category, and healthy weight range are calculated instantly.
5. View where you fall on the visual BMI scale bar.

What is Body Mass Index (BMI)?

Body Mass Index (BMI) is a numerical value derived from a person's weight and height that provides a quick estimate of whether they fall into an underweight, normal, overweight, or obese category. Originally developed by Belgian mathematician Adolphe Quetelet in the 1830s, BMI has become one of the most widely used screening tools in public health and clinical medicine. The World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC), and healthcare providers around the world rely on BMI as a first step in assessing weight-related health risks. While it does not measure body fat directly, it serves as an accessible and cost-free way to flag potential concerns for further evaluation.

How BMI is Calculated

The BMI formula divides your weight by the square of your height. In metric units, the calculation is BMI = weight (kg) / height (m)². For imperial units, the formula is BMI = 703 x weight (lbs) / height (in)². For example, a person who weighs 70 kg and stands 1.75 m tall has a BMI of 70 / (1.75 x 1.75) = 22.9. This calculator performs the conversion automatically regardless of which unit system you choose. It also displays the healthy weight range for your specific height, based on a BMI between 18.5 and 24.9, so you can see exactly how much you would need to gain or lose to reach the normal classification.

Common Use Cases

• Initial health screenings at doctor's offices and clinics
• Setting a baseline before starting a weight loss or fitness program
• Tracking weight changes over time alongside other health markers
• Population-level health research and epidemiological studies
• Insurance and workplace wellness assessments
• Personal goal-setting when combined with body fat or waist circumference data

BMI Categories Explained

The WHO defines four primary BMI categories for adults. A BMI below 18.5 is classified as underweight, which may indicate malnutrition, an eating disorder, or an underlying medical condition. A BMI between 18.5 and 24.9 falls within the normal range, where the risk of weight-related diseases such as type 2 diabetes, hypertension, and cardiovascular disease is generally lowest. A BMI of 25 to 29.9 is classified as overweight, indicating elevated risk for chronic conditions. A BMI of 30 or above is classified as obese, with subcategories of Class I (30 to 34.9), Class II (35 to 39.9), and Class III (40 and above, sometimes called severe or morbid obesity).

It is important to recognize the limitations of BMI. It does not distinguish between muscle mass and fat mass, so athletes and highly muscular individuals may register as overweight or obese despite having low body fat. BMI also does not account for fat distribution; carrying excess fat around the waist (visceral fat) is more dangerous than carrying it in the hips and thighs. Age, sex, and ethnicity can also influence what constitutes a healthy range. For these reasons, BMI should be used as one piece of a broader health assessment, not as a definitive diagnosis. Always consult a healthcare professional for personalized guidance.

Related Health Tools

To build a more complete picture of your health, estimate your daily energy needs with our Calorie Calculator, measure your composition with the Body Fat Calculator, find your target with the Ideal Weight Calculator, or determine your total daily calorie burn with the TDEE Calculator.