BMI Calculator Calculate your Body Mass Index based on height and weight with metric and imperial units.
BMI Calculator
Calculate your Body Mass Index based on height and weight with metric and imperial units.
Choose Unit System
Select metric (kg/cm) or imperial (lbs/ft-in).
Enter Your Measurements
Input your weight and height.
View Your BMI
See your BMI value, category, and the BMI reference chart.
What Is BMI Calculator?
The Body Mass Index (BMI) calculator is a widely used screening tool that estimates body fat based on height and weight. Developed by Belgian mathematician Adolphe Quetelet in the 1830s, BMI provides a simple numerical measure that categorizes individuals into underweight, normal weight, overweight, and obese ranges. The formula divides weight by the square of height. While BMI does not directly measure body fat percentage, it correlates well with more direct measures of body fat for most people. Healthcare professionals use BMI as an initial screening tool to identify potential weight-related health risks. This calculator supports both metric and imperial systems, provides the BMI category, and shows the full reference chart so you can understand where you fall on the spectrum.
Why Use BMI Calculator?
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Quick health screening tool recommended by WHO and medical professionals
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Supports both metric (kg/cm) and imperial (lbs/ft-in) units
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Shows BMI category with color-coded results
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Displays the complete BMI reference chart for context
Common Use Cases
Health Screening
Use as a first step in assessing weight-related health risks.
Fitness Tracking
Monitor BMI changes over time as part of a fitness program.
Medical Assessments
Healthcare providers use BMI as part of routine check-ups.
Insurance Applications
Many insurance applications require BMI information.
Technical Guide
BMI is calculated using the formula: BMI = weight(kg) / height(m)² for metric units, or BMI = (weight(lbs) / height(in)²) × 703 for imperial units. The WHO classification defines BMI < 18.5 as underweight, 18.5-24.9 as normal weight, 25.0-29.9 as overweight, and 30+ as obese, with further subcategories. BMI has limitations — it does not distinguish between muscle mass and fat mass, so athletes with high muscle mass may have elevated BMIs despite low body fat. It also does not account for age, sex, ethnicity, or body composition. For a more complete picture, BMI should be used alongside other measurements like waist circumference, body fat percentage, and clinical assessments.
Tips & Best Practices
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1BMI is a screening tool, not a diagnostic — consult a healthcare provider for medical advice
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2Athletes and muscular individuals may have elevated BMI despite healthy body fat levels
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3BMI categories may vary slightly for Asian populations (overweight starts at 23)
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4For children, BMI is age- and sex-specific (BMI-for-age percentiles)
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🔢 Math & CalculatorsFrequently Asked Questions
Q What is a healthy BMI range?
Q Is BMI accurate for athletes?
Q How is BMI calculated?
Q Does BMI differ by age?
Q What BMI is considered obese?
About This Tool
BMI Calculator is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.