Free BMI Calculator — Body Mass Index Online
Calculate your BMI (Body Mass Index) free. Supports metric (kg/cm) and imperial (lbs/ft). Shows WHO health categories. Instant results, no sign-up needed.
BMI Calculator Tool
How to Use BMI Calculator — Step by Step
- 1Select Measurement System
Choose metric (kg/cm) or imperial (lbs/ft/in) based on your preference.
- 2Enter Height
Input your height in centimeters (metric) or feet and inches (imperial).
- 3Enter Weight
Input your weight in kilograms (metric) or pounds (imperial).
- 4Calculate
Click Calculate to see your BMI value and WHO health category.
Supported Formats & Options
Complete Guide to BMI Calculator
Body Mass Index (BMI) is a widely used screening tool for assessing whether a person's weight is in a healthy range relative to their height. Developed in the 19th century by Belgian mathematician Adolphe Quetelet, BMI has become the standard measurement used by healthcare professionals, public health researchers, and fitness practitioners worldwide.
The BMI formula is: BMI = weight (kg) / height² (m²). In imperial units: BMI = (weight in lbs × 703) / height² (inches). Our calculator automatically converts between metric and imperial units.
The World Health Organization (WHO) defines BMI categories as follows: Underweight: BMI below 18.5. Normal weight: BMI 18.5 to 24.9. Overweight: BMI 25.0 to 29.9. Obesity Class I: BMI 30.0 to 34.9. Obesity Class II: BMI 35.0 to 39.9. Obesity Class III (severe): BMI 40.0 and above.
BMI limitations: While BMI is a useful population-level screening metric, it has important limitations for individuals. BMI doesn't account for muscle mass — a highly muscular athlete may have a high BMI but very low body fat. It also doesn't distinguish between different types of body fat or their distribution. Age and sex can also affect the relationship between BMI and health risk. Elderly people tend to have more body fat at the same BMI as younger adults.
Despite its limitations, BMI remains valuable as an initial screening tool. If your BMI falls outside the normal range, it's worth discussing with a healthcare provider. They can assess additional factors like waist circumference, body composition, blood pressure, and lifestyle factors to get a complete picture of your health.
Regular monitoring of your BMI over time can help track progress during weight management programs. However, always use BMI as one data point among many, not as the sole measure of health.
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Frequently Asked Questions about BMI Calculator
BMI is a useful screening tool but not a direct measure of body fat or overall health. It doesn't account for muscle mass, body composition, age, sex, or where fat is distributed. It's best used as one indicator among several in a comprehensive health assessment.
According to the World Health Organization, a normal (healthy) BMI is between 18.5 and 24.9. Below 18.5 is considered underweight, 25-29.9 is overweight, and 30+ is classified as obese.
Yes. Highly muscular athletes may have a BMI in the overweight or obese range despite having very low body fat, because muscle is denser and heavier than fat. For athletes, body composition measurements like body fat percentage are more accurate.
This calculator is designed for adults (18+ years). For children and teenagers, BMI interpretation uses age- and sex-specific percentile charts (BMI-for-age) which are different from adult standards. Consult a pediatrician for children's BMI assessment.