The height to weight ratio is one of the most common ways to assess physical health and body composition. This tool uses two primary metrics: Body Mass Index (BMI) and Ideal Body Weight (IBW).
How BMI is Calculated
BMI is a standardized measurement used by health professionals globally to categorize individuals into weight groups. The formula is:
BMI = Weight (kg) / [Height (m)]²
If you are using the Imperial system, the formula is: 703 × weight (lbs) / [height (in)]².
BMI Categories Table
BMI Range
Category
Below 18.5
Underweight
18.5 – 24.9
Normal weight
25.0 – 29.9
Overweight
30.0 and above
Obese
What is Ideal Body Weight (IBW)?
Our calculator uses the Devine Formula, which is the most widely used equation in clinical settings for estimating ideal weight based on height and gender. It assumes a base weight for 5 feet (60 inches) of height and adds a specific amount for every additional inch.
Men: 50.0 kg + 2.3 kg for each inch over 5 feet.
Women: 45.5 kg + 2.3 kg for each inch over 5 feet.
Why This Matters
While these numbers are excellent screening tools, it is important to remember that BMI does not distinguish between muscle mass and body fat. Athletes with high muscle density may have a "high" BMI despite having low body fat. Always consult with a healthcare professional before making significant lifestyle changes.
function toggleUnitInputs() {
var system = document.getElementById('unit_system').value;
var metricDiv = document.getElementById('metric-inputs');
var imperialDiv = document.getElementById('imperial-inputs');
if (system === 'metric') {
metricDiv.style.display = 'block';
imperialDiv.style.display = 'none';
} else {
metricDiv.style.display = 'none';
imperialDiv.style.display = 'block';
}
}
function calculateMetrics() {
var system = document.getElementById('unit_system').value;
var gender = document.getElementById('gender').value;
var weight, heightCm, heightInches;
if (system === 'metric') {
weight = parseFloat(document.getElementById('weight_kg').value);
heightCm = parseFloat(document.getElementById('height_cm').value);
if (isNaN(weight) || isNaN(heightCm) || heightCm <= 0) {
alert("Please enter valid weight and height values.");
return;
}
heightInches = heightCm / 2.54;
} else {
var lbs = parseFloat(document.getElementById('weight_lb').value);
var ft = parseFloat(document.getElementById('height_ft').value) || 0;
var inch = parseFloat(document.getElementById('height_in').value) || 0;
if (isNaN(lbs) || (ft === 0 && inch === 0)) {
alert("Please enter valid weight and height values.");
return;
}
weight = lbs * 0.453592; // to kg
heightInches = (ft * 12) + inch;
heightCm = heightInches * 2.54;
}
// BMI Calculation
var heightMeters = heightCm / 100;
var bmi = weight / (heightMeters * heightMeters);
// BMI Category
var category = "";
if (bmi < 18.5) category = "Underweight";
else if (bmi < 25) category = "Normal weight";
else if (bmi < 30) category = "Overweight";
else category = "Obese";
// IBW Calculation (Devine Formula)
var ibw;
var baseInches = heightInches – 60;
if (baseInches < 0) baseInches = 0; // Formula usually applied for 5ft+
if (gender === 'male') {
ibw = 50 + (2.3 * baseInches);
} else {
ibw = 45.5 + (2.3 * baseInches);
}
// Ponderal Index (more sensitive for very short/tall)
var pi = weight / Math.pow(heightMeters, 3);
// Display Results
document.getElementById('bmi-val').innerText = bmi.toFixed(1);
document.getElementById('bmi-cat').innerText = category;
if (system === 'metric') {
document.getElementById('ibw-val').innerText = (ibw * 0.9).toFixed(1) + " kg – " + (ibw * 1.1).toFixed(1) + " kg";
} else {
var ibwLb = ibw * 2.20462;
document.getElementById('ibw-val').innerText = (ibwLb * 0.9).toFixed(1) + " lbs – " + (ibwLb * 1.1).toFixed(1) + " lbs";
}
document.getElementById('pi-val').innerText = pi.toFixed(2) + " kg/m³";
document.getElementById('results-area').style.display = 'block';
// Smooth scroll to results
document.getElementById('results-area').scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}