BMI Calculator — Calculate Your Body Mass Index Free
PopularCalculate your Body Mass Index instantly
Calculate BMI using metric (kg/cm) or imperial (lbs/ft) units. Get your BMI category, health range, and personalized insights.
About BMI Calculator
Body Mass Index (BMI) is a widely used screening metric that estimates whether a person's weight is appropriate for their height. Calculated by dividing weight in kilograms by height in metres squared, it provides a quick, population-level indicator of weight categories associated with health risks.
The BMI scale was developed by Belgian mathematician Adolphe Quetelet in the 19th century and adopted by the World Health Organisation as a standard classification system. The four main categories are: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25–29.9), and Obese (30 and above). Some systems further subdivide the obese category into Class I, II, and III.
BMI is commonly used by healthcare providers for initial patient screening, by public health researchers for population studies, by fitness professionals for tracking client progress, and by individuals monitoring their own weight management goals.
Important limitations: BMI does not measure body fat percentage directly. Highly muscular individuals may register as overweight despite low body fat, while sedentary individuals with low muscle mass may fall within a "normal" BMI range despite elevated health risks. Children require age- and sex-adjusted BMI percentiles. Ethnic-specific thresholds also exist — for example, some health organisations recommend lower BMI thresholds for Asian populations. Always interpret results alongside professional medical advice.
Frequently Asked Questions
What is a healthy BMI range?
The World Health Organisation defines healthy BMI as 18.5–24.9. Below 18.5 is considered underweight; 25–29.9 is overweight; 30 and above is obese. These thresholds are general guidelines and do not account for age, sex, ethnicity, or muscle mass.
Is BMI an accurate measure of health?
BMI is a useful screening tool but not a complete measure of health. It does not distinguish between fat mass and muscle mass — a muscular athlete may have a high BMI without excess body fat. Always consult a healthcare professional for a full health assessment.
What units does this calculator support?
Both metric (kilograms and centimetres) and imperial (pounds, feet, and inches) units are supported. Select your preferred unit system at the top of the calculator.
How is BMI calculated?
BMI = weight (kg) ÷ height² (m²). In imperial units: BMI = (weight in lbs × 703) ÷ height² (in²).