function toggleBmiUnits() {
var radios = document.getElementsByName('unitSystem');
var metricDiv = document.getElementById('metricInputs');
var imperialDiv = document.getElementById('imperialInputs');
var selectedValue;
for (var i = 0; i < radios.length; i++) {
if (radios[i].checked) {
selectedValue = radios[i].value;
break;
}
}
if (selectedValue === 'metric') {
metricDiv.style.display = 'block';
imperialDiv.style.display = 'none';
} else {
metricDiv.style.display = 'none';
imperialDiv.style.display = 'block';
}
// Hide previous results when switching
document.getElementById('bmiResult').style.display = 'none';
}
function calculateBMI() {
var radios = document.getElementsByName('unitSystem');
var system = 'metric';
for (var i = 0; i < radios.length; i++) {
if (radios[i].checked) {
system = radios[i].value;
break;
}
}
var bmi = 0;
var valid = true;
if (system === 'metric') {
var weightKg = parseFloat(document.getElementById('weightMetric').value);
var heightCm = parseFloat(document.getElementById('heightMetric').value);
if (isNaN(weightKg) || weightKg <= 0 || isNaN(heightCm) || heightCm <= 0) {
valid = false;
} else {
var heightM = heightCm / 100;
bmi = weightKg / (heightM * heightM);
}
} else {
var weightLbs = parseFloat(document.getElementById('weightImperial').value);
var feet = parseFloat(document.getElementById('heightFeet').value);
var inches = parseFloat(document.getElementById('heightInches').value);
// Handle empty inches as 0 if feet is provided
if (isNaN(inches)) inches = 0;
if (isNaN(weightLbs) || weightLbs <= 0 || isNaN(feet) || feet < 0) {
valid = false;
} else {
var totalInches = (feet * 12) + inches;
if (totalInches <= 0) {
valid = false;
} else {
// BMI Formula Imperial: 703 * weight(lbs) / height(in)^2
bmi = 703 * (weightLbs / (totalInches * totalInches));
}
}
}
var resultDiv = document.getElementById('bmiResult');
if (!valid) {
resultDiv.style.display = 'block';
resultDiv.style.backgroundColor = '#ffebee';
resultDiv.style.border = '1px solid #ef5350';
resultDiv.innerHTML = 'Please enter valid positive numbers for weight and height.';
return;
}
// Round to 1 decimal place
bmi = Math.round(bmi * 10) / 10;
var category = ";
var colorCode = ";
if (bmi = 18.5 && bmi = 25 && bmi <= 29.9) {
category = 'Overweight';
colorCode = '#f1c40f'; // Yellow/Orange
} else {
category = 'Obesity';
colorCode = '#e74c3c'; // Red
}
resultDiv.style.display = 'block';
resultDiv.style.backgroundColor = '#fff';
resultDiv.style.border = '1px solid ' + colorCode;
resultDiv.innerHTML =
'Your BMI Score:' +
'' + bmi + '' +
'Category: ' + category + '';
}
How to Calculate BMI Rate: Understanding Your Body Mass Index
Understanding how to calculate BMI rate is one of the quickest ways to assess your body composition and determine if you are within a healthy weight range. The Body Mass Index (BMI) is a screening tool used worldwide by health professionals to categorize weight groups based on height and mass. Whether you are looking to lose weight, gain muscle, or simply maintain a healthy lifestyle, knowing your BMI is a fundamental starting point.
What is the BMI Formula?
The BMI calculation is purely mathematical. It does not measure body fat directly but uses your weight and height to provide a proxy measure. There are two primary formulas used depending on the measurement system:
1. The Metric BMI Formula
This is the standard formula used in most of the world and in scientific research.
BMI = Weight (kg) / [Height (m)]²
Example: A person weighing 70 kg who is 1.75 meters tall would calculate: 70 / (1.75 × 1.75) = 22.9.
2. The Imperial BMI Formula
Commonly used in the United States, this formula adjusts for pounds and inches.
BMI = 703 × Weight (lbs) / [Height (in)]²
Example: A person weighing 160 lbs who is 5 feet 9 inches (69 inches) tall would calculate: 703 × 160 / (69 × 69) = 23.6.
Interpreting Your BMI Results
Once you know how to calculate your BMI rate, the next step is interpreting the number. The World Health Organization (WHO) has established standard categories for adults:
BMI Range
Weight Category
Below 18.5
Underweight
18.5 – 24.9
Normal Weight
25.0 – 29.9
Overweight
30.0 and Above
Obesity
Limitations of BMI
While learning how to calculate BMI rate is useful, it is important to recognize its limitations. BMI is a simple calculation that does not distinguish between muscle mass and fat mass. Consequently:
Athletes: Individuals with high muscle mass may be categorized as "overweight" or "obese" despite having low body fat, because muscle is denser than fat.
Elderly: Older adults may have a "normal" BMI but possess higher body fat and lower muscle mass (sarcopenia).
Bone Density: BMI does not account for variations in bone structure or frame size.
Why Monitor Your BMI?
Despite its limitations, BMI correlates reasonably well with body fat for the general population. A high BMI is often a risk factor for diseases such as heart disease, high blood pressure, type 2 diabetes, gallstones, breathing problems, and certain cancers. Conversely, being underweight can lead to nutritional deficiencies, osteoporosis, and a weakened immune system.
Use the calculator above to regularly monitor your status. If your result falls outside the "Normal Weight" range, consider consulting a healthcare provider to discuss whether your weight might be affecting your overall health and what steps you can take to achieve your wellness goals.