BMI Calculator

Calculate Body Mass Index from height and weight with interpretations, healthy weight ranges, and health context.

100% client-side No signup Free forever
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BMI Categories

CategoryBMI Range
UnderweightLess than 18.5
Normal weight18.5 - 24.9
Overweight25 - 29.9
Obese30 or greater
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How to Use BMI Calculator

How to Use the BMI Calculator

  1. Select measurement units: Choose between Metric (kg/cm) or Imperial (lb/inches) units.
  2. Enter your height: Input your height in the selected units.
  3. Enter your weight: Input your current weight in the selected units.
  4. Click Calculate BMI: Press the button to compute your Body Mass Index.
  5. View your results: See your BMI number, weight category, and healthy weight range for your height.

BMI Formula

  • Metric: BMI = weight (kg) ÷ height² (m²)
  • Imperial: BMI = weight (lb) × 703 ÷ height² (inches²)

Example Calculation

For a person who is 170 cm tall and weighs 70 kg:
BMI = 70 ÷ (1.70 × 1.70) = 70 ÷ 2.89 = 24.2 (Normal weight)

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Features

  • Metric and Imperial unit support
  • BMI category classification
  • Healthy weight range for your height
  • Visual BMI chart and scale
  • Color-coded results
  • Health risk information
  • Underweight to Obese III categories
  • Instant calculation
  • Mobile-friendly design
  • Privacy focused - no data stored
  • WHO standard categories
  • Free with no registration
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About BMI Calculator

Body Mass Index provides a quick screening metric relating weight to height, used worldwide in medical settings as an initial health indicator. Our BMI Calculator computes your index instantly while explaining what the numbers mean and their limitations.

BMI Categories

  • Underweight: BMI below 18.5 may indicate nutritional deficiency
  • Normal Weight: BMI 18.5-24.9 associates with lowest health risks
  • Overweight: BMI 25-29.9 indicates elevated health risks
  • Obese Class I: BMI 30-34.9
  • Obese Class II: BMI 35-39.9
  • Obese Class III: BMI 40 and above

Important Context

BMI is a population-level screening tool, not a diagnostic measure. It doesn't distinguish muscle from fat—athletes may register as "overweight" despite low body fat. Age, sex, ethnicity, and body composition all affect what's healthy for individuals. A high BMI warrants further assessment, not automatic diagnosis.

Healthy Weight Range

Based on your height, we calculate the weight range corresponding to a BMI of 18.5-24.9. This provides a general target, but individual factors—bone structure, muscle mass, age—mean your optimal weight may differ. Consult healthcare providers for personalized guidance.

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Frequently Asked Questions

What is BMI and what does it measure?
BMI (Body Mass Index) is a simple measure using height and weight: BMI = weight(kg) / height(m)². It provides a rough indicator of body fat and health risk categories. While useful for population health, it doesn't distinguish between muscle and fat or account for body composition.
What are the BMI categories?
Standard WHO categories: Underweight (<18.5), Normal (18.5-24.9), Overweight (25-29.9), Obese Class I (30-34.9), Obese Class II (35-39.9), Obese Class III (40+). These thresholds may vary slightly by region and are adjusted for children and teens using age-specific percentiles.
Is BMI accurate for everyone?
BMI has limitations: it overestimates fat in muscular people (athletes may show "overweight"), underestimates in elderly with muscle loss, and doesn't account for fat distribution (visceral vs subcutaneous). It's a screening tool, not a diagnosis. Consider waist circumference and body composition for complete picture.
How do I calculate BMI manually?
Metric: BMI = weight in kg ÷ (height in meters)². Imperial: BMI = (weight in pounds × 703) ÷ (height in inches)². Example: 70kg, 1.75m → 70 ÷ 1.75² = 22.9. Our calculator handles unit conversion automatically - enter values in any unit system.
What weight should I aim for based on my height?
Our calculator shows the healthy weight range for your height (BMI 18.5-24.9). For example, at 170cm, healthy weight is roughly 53-72kg. We also show how much weight change would move you between categories. Remember these are guidelines - consult healthcare providers for personalized advice.
Is child BMI calculated differently?
Yes! Children's BMI uses the same formula but interprets results using age and sex-specific growth charts (percentiles). A BMI of 22 means different things for an adult vs a 10-year-old. Our calculator offers pediatric BMI mode with appropriate percentile interpretation.