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Body Mass Index (BMI) Calculator

The Body Mass Index (BMI) is a widely used screening tool that helps assess whether a person has a healthy body weight in proportion to their height. It's a simple calculation that uses your weight and height to estimate your body fat. While not a direct measure of body fat, BMI is an inexpensive and easy-to-perform method for categorizing weight status for adults.

Understanding BMI Categories

BMI values are categorized as follows for most adults:

  • Underweight: Less than 18.5
  • Normal weight: 18.5 – 24.9
  • Overweight: 25 – 29.9
  • Obesity: 30 or greater

These categories are general guidelines. For example, a very muscular person might have a high BMI without being overweight, as muscle weighs more than fat. Conversely, an elderly person with low muscle mass might have a normal BMI but still have excess body fat. Therefore, BMI should be considered alongside other health assessments like waist circumference, body composition, and overall health conditions.

How BMI is Calculated

The formula for BMI depends on the units of measurement used:

  • Metric System: BMI = weight (kg) / [height (m)]²
  • Imperial System: BMI = [weight (lbs) / height (inches)²] * 703

Our calculator below allows you to easily compute your BMI using either metric or imperial units. Simply enter your weight and height, select your preferred unit system, and click "Calculate BMI".

Limitations of BMI

While useful, BMI has limitations:

  • It does not distinguish between fat mass and muscle mass.
  • It may not accurately reflect body fat percentage in certain populations (e.g., athletes, elderly, pregnant women).
  • It doesn't account for fat distribution (e.g., abdominal fat is more dangerous than fat on hips).
  • Ethnic differences in body composition are not fully captured.

Always consult with a healthcare professional for a comprehensive assessment of your health and weight status.

Calculate Your BMI

function toggleUnitInputs() { var metricInputs = document.getElementById('metricInputs'); var imperialInputs = document.getElementById('imperialInputs'); var unitMetric = document.getElementById('unitMetric'); if (unitMetric.checked) { metricInputs.style.display = 'block'; imperialInputs.style.display = 'none'; } else { metricInputs.style.display = 'none'; imperialInputs.style.display = 'block'; } // Clear previous results when units are toggled document.getElementById('bmiResult').innerHTML = "; } function calculateBMI() { var unitMetric = document.getElementById('unitMetric').checked; var weight, height, bmi, category; var resultDiv = document.getElementById('bmiResult'); resultDiv.style.color = '#333'; // Reset color if (unitMetric) { // Metric calculation weight = parseFloat(document.getElementById('weightKg').value); height = parseFloat(document.getElementById('heightCm').value); if (isNaN(weight) || isNaN(height) || weight <= 0 || height <= 0) { resultDiv.innerHTML = 'Please enter valid positive numbers for weight (kg) and height (cm).'; return; } var heightMeters = height / 100; bmi = weight / (heightMeters * heightMeters); } else { // Imperial calculation weight = parseFloat(document.getElementById('weightLbs').value); height = parseFloat(document.getElementById('heightInches').value); if (isNaN(weight) || isNaN(height) || weight <= 0 || height <= 0) { resultDiv.innerHTML = 'Please enter valid positive numbers for weight (lbs) and height (inches).'; return; } bmi = (weight / (height * height)) * 703; } // Determine BMI category if (bmi = 18.5 && bmi = 25 && bmi = 30 category = 'Obesity'; resultDiv.style.color = '#dc3545'; // Red for obesity } resultDiv.innerHTML = 'Your BMI is: ' + bmi.toFixed(2) + 'Category: ' + category + ''; } // Initialize the correct input display on load window.onload = function() { toggleUnitInputs(); };

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