Free Adult BMI Calculator
Accurately calculate your Body Mass Index in seconds. Choose between US imperial units (feet, inches, pounds) and metric standards (cm, kg).
Calculate Your Body Mass Index
Enter your height and weight below for an immediate, private calculation.
How to Get the Most Accurate BMI Reading
Measure Height Barefoot
Stand straight against a flat wall with shoes removed. Looking straight ahead ensures your recorded height is exact.
Weigh in the Morning
Weigh yourself first thing in the morning after using the restroom and before breakfast for the most consistent day-to-day comparison.
Review the Scale
Compare your calculated number with the adult classification scale below to understand your clinical weight bracket.
Adult BMI Reference Ranges
World Health Organization (WHO) Adult BMI Classifications
Standard international adult reference ranges. Note that BMI is an epidemiological screening metric and should be evaluated alongside individual clinical indicators.
| Category | BMI Range (kg/m²) | Classification Status | General Health Assessment |
|---|---|---|---|
| Severe Thinness | < 16.0 | Underweight (Severe) | Elevated risk of nutrient deficiencies and low bone mineral density |
| Moderate Thinness | 16.0 – 16.9 | Underweight (Moderate) | Increased risk of nutritional compromise and fatigue |
| Mild Thinness | 17.0 – 18.4 | Underweight (Mild) | Mild risk; may be typical for some lean body types |
| Normal / Healthy Weight | 18.5 – 24.9 | Healthy Weight | Statistically lowest correlation with weight-related chronic conditions |
| Pre-Obesity / Overweight | 25.0 – 29.9 | Overweight | Slightly elevated cardiovascular and metabolic risk; evaluate body composition |
| Obesity Class I | 30.0 – 34.9 | Obesity (Class 1) | Moderate risk of hypertension, dyslipidemia, and type 2 diabetes |
| Obesity Class II | 35.0 – 39.9 | Obesity (Class 2) | Severe risk of cardiovascular complications and sleep apnea |
| Obesity Class III | ≥ 40.0 | Obesity (Class 3 / Severe) | Very severe health risk; comprehensive clinical management recommended |
Clinical context: These cutoffs apply to adults age 20 and older. Some health organizations (such as the WHO Asian expert consultation) suggest alternative cutoffs (such as overweight beginning at 23.0 and obesity at 27.5) for populations with differing body fat distributions.
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Frequently Asked Questions About BMI
Find clear, evidence-based answers to common questions about Body Mass Index calculation, accuracy, and interpretation.
Select your preferred measurement system (US Units or Metric). Input your height in feet and inches (or centimeters) and your weight in pounds (or kilograms). Click 'Calculate BMI' or press Enter on your keyboard to instantly see your BMI score, weight category, and target healthy weight range.