function updateHeightUnit() {
var weightUnit = document.getElementById('weightUnit').value;
var heightUnitSelect = document.getElementById('heightUnit');
if (weightUnit === 'kg') {
heightUnitSelect.value = 'cm';
} else {
heightUnitSelect.value = 'inches';
}
}
function updateWeightUnit() {
var heightUnit = document.getElementById('heightUnit').value;
var weightUnitSelect = document.getElementById('weightUnit');
if (heightUnit === 'cm') {
weightUnitSelect.value = 'kg';
} else {
weightUnitSelect.value = 'lbs';
}
}
function calculateBMI() {
var weight = parseFloat(document.getElementById('weightInput').value);
var height = parseFloat(document.getElementById('heightInput').value);
var weightUnit = document.getElementById('weightUnit').value;
var heightUnit = document.getElementById('heightUnit').value;
var bmiResultDiv = document.getElementById('bmiResult');
if (isNaN(weight) || isNaN(height) || weight <= 0 || height <= 0) {
bmiResultDiv.innerHTML = "Please enter valid positive numbers for weight and height.";
return;
}
var weight_kg;
var height_m;
var bmi;
var minIdealWeight_kg;
var maxIdealWeight_kg;
if (weightUnit === 'kg' && heightUnit === 'cm') {
weight_kg = weight;
height_m = height / 100;
} else if (weightUnit === 'lbs' && heightUnit === 'inches') {
weight_kg = weight * 0.453592; // lbs to kg
height_m = height * 0.0254; // inches to meters
} else {
bmiResultDiv.innerHTML = "Unit mismatch. Please select kg/cm or lbs/inches.";
return;
}
bmi = weight_kg / (height_m * height_m);
var bmiCategory = "";
var categoryColor = "";
if (bmi = 18.5 && bmi = 25 && bmi = 30 && bmi = 35 && bmi < 39.9) {
bmiCategory = "Obese Class II";
categoryColor = "darkred";
} else {
bmiCategory = "Obese Class III (Morbidly Obese)";
categoryColor = "darkred";
}
// Calculate ideal weight range based on normal BMI (18.5 to 24.9)
minIdealWeight_kg = 18.5 * (height_m * height_m);
maxIdealWeight_kg = 24.9 * (height_m * height_m);
var idealWeightRangeText = "";
if (weightUnit === 'kg') {
idealWeightRangeText = minIdealWeight_kg.toFixed(1) + " kg – " + maxIdealWeight_kg.toFixed(1) + " kg";
} else { // lbs
var minIdealWeight_lbs = minIdealWeight_kg / 0.453592;
var maxIdealWeight_lbs = maxIdealWeight_kg / 0.453592;
idealWeightRangeText = minIdealWeight_lbs.toFixed(1) + " lbs – " + maxIdealWeight_lbs.toFixed(1) + " lbs";
}
bmiResultDiv.innerHTML =
"Your BMI is: " + bmi.toFixed(2) + "" +
"Category: " + bmiCategory + "" +
"For your height, a healthy weight range is approximately: " + idealWeightRangeText + "";
}
// Initial unit synchronization
document.addEventListener('DOMContentLoaded', function() {
updateHeightUnit();
});
.calculator-container {
background-color: #f9f9f9;
border: 1px solid #ddd;
padding: 20px;
border-radius: 8px;
max-width: 500px;
margin: 20px auto;
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}
.calculator-container h2 {
text-align: center;
color: #333;
margin-bottom: 20px;
}
.calc-input-group {
margin-bottom: 15px;
display: flex;
align-items: center;
gap: 10px;
}
.calc-input-group label {
flex: 1;
font-weight: bold;
color: #555;
}
.calc-input-group input[type="number"],
.calc-input-group select {
flex: 2;
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
}
.calculate-button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
cursor: pointer;
transition: background-color 0.3s ease;
margin-top: 20px;
}
.calculate-button:hover {
background-color: #0056b3;
}
.calc-result {
margin-top: 25px;
padding: 15px;
background-color: #e9f7ef;
border: 1px solid #d4edda;
border-radius: 5px;
color: #155724;
font-size: 17px;
line-height: 1.6;
}
.calc-result p {
margin: 5px 0;
}
.calc-result strong {
font-weight: bold;
}
.calc-result .error {
color: #721c24;
background-color: #f8d7da;
border-color: #f5c6cb;
padding: 10px;
border-radius: 4px;
}
Understanding Your Body Mass Index (BMI)
The Body Mass Index (BMI) is a widely used screening tool that helps assess whether a person has a healthy weight relative to their height. While it doesn't directly measure body fat, it provides a useful indicator for many individuals and is often the first step in evaluating potential weight-related health risks.
How is BMI Calculated?
The BMI is calculated using a simple formula based on your weight and height:
Our advanced BMI calculator above allows you to input your measurements in either kilograms and centimeters or pounds and inches, automatically performing the correct calculation for you.
BMI Categories and What They Mean
Once your BMI is calculated, it falls into one of several categories established by health organizations like the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC):
Underweight: BMI less than 18.5
Normal weight: BMI between 18.5 and 24.9
Overweight: BMI between 25 and 29.9
Obese Class I: BMI between 30 and 34.9
Obese Class II: BMI between 35 and 39.9
Obese Class III (Morbidly Obese): BMI of 40 or greater
These categories are general guidelines. For instance, a BMI in the "normal weight" range is generally associated with the lowest risk of various diseases.
Limitations of BMI
While BMI is a convenient tool, it has limitations and should not be the sole determinant of health. It does not account for:
Body Composition: A very muscular person (e.g., an athlete) might have a high BMI due to muscle mass, not excess fat, and could be classified as "overweight" or "obese" despite being very healthy.
Fat Distribution: Where fat is stored on the body (e.g., around the waist vs. hips) can impact health risks, but BMI doesn't differentiate this.
Age, Sex, and Ethnicity: These factors can influence body composition and health risks, but the standard BMI formula doesn't adjust for them. For example, older adults may have less muscle mass, and certain ethnic groups may have different healthy BMI ranges.
When is BMI Useful?
Despite its limitations, BMI remains a valuable screening tool for:
Population Health Studies: Tracking obesity trends across large groups.
Initial Health Assessments: Providing a quick indicator for healthcare professionals to decide if further evaluation (like body fat percentage, waist circumference, or blood tests) is needed.
Identifying Risk: For most people, a high BMI correlates with higher body fat and increased risk for conditions like heart disease, type 2 diabetes, and certain cancers.
Example Calculation
Let's consider an example:
Scenario 1: Metric Units
Weight: 70 kg
Height: 1.75 m (175 cm)
BMI = 70 / (1.75 * 1.75) = 70 / 3.0625 = 22.86
Category: Normal weight
Ideal Weight Range (for 1.75m height): 18.5 * (1.75^2) to 24.9 * (1.75^2) = 56.6 kg to 76.2 kg
Ideal Weight Range (for 70 inches height): 18.5 * (1.778^2) to 24.9 * (1.778^2) (converted to kg/m) = 58.4 kg to 78.7 kg, which is approximately 128.7 lbs to 173.5 lbs.
Use the calculator above to find your own BMI and understand its implications for your health. Remember to consult with a healthcare professional for personalized advice regarding your weight and health goals.