Body Mass Index (BMI) is a numerical value derived from the mass (weight) and height of an individual. It is a widely used screening tool to categorize a person's weight status relative to their height, helping to identify potential weight categories that may increase the risk of certain health problems. BMI is calculated using a simple formula:
BMI = (weight in kilograms) / (height in meters)2
While BMI is a convenient and cost-effective measure, it's important to remember that it is a screening tool and not a diagnostic one. It does not account for body composition (e.g., muscle mass vs. fat mass), bone density, or body fat distribution, which can influence health outcomes.
Understanding BMI Categories
The World Health Organization (WHO) and other health authorities use standard categories to interpret BMI values for adults:
Underweight: BMI less than 18.5
Normal weight: BMI between 18.5 and 24.9
Overweight: BMI between 25.0 and 29.9
Obesity Class I: BMI between 30.0 and 34.9
Obesity Class II: BMI between 35.0 and 39.9
Obesity Class III (Severe Obesity): BMI 40.0 or greater
Why is BMI Important?
Maintaining a healthy weight, as indicated by a BMI within the normal range, is crucial for overall health and well-being. Both underweight and overweight/obesity are associated with an increased risk of various health complications:
Risks associated with Overweight/Obesity: Heart disease, stroke, type 2 diabetes, certain types of cancer, high blood pressure, sleep apnea, osteoarthritis, and fatty liver disease.
Risks associated with Underweight: Malnutrition, osteoporosis, infertility, weakened immune system, and increased risk of complications from surgery or illness.
Regularly monitoring your BMI can be a proactive step in managing your health. If your BMI falls outside the normal range, it is recommended to consult with a healthcare professional to discuss appropriate lifestyle changes, diet, and exercise plans.
How to Use This Calculator
This calculator simplifies the process of determining your BMI. Simply enter your current weight in kilograms and your height in centimeters into the fields provided. Click the "Calculate BMI" button, and the tool will instantly display your BMI value and its corresponding health category. This allows for a quick and easy assessment of your weight status.
function calculateBMI() {
var weightKgInput = document.getElementById("weightKg");
var heightCmInput = document.getElementById("heightCm");
var resultDiv = document.getElementById("result");
var resultCategoryDiv = document.getElementById("resultCategory");
var weightKg = parseFloat(weightKgInput.value);
var heightCm = parseFloat(heightCmInput.value);
if (isNaN(weightKg) || isNaN(heightCm) || weightKg <= 0 || heightCm <= 0) {
resultDiv.innerHTML = "Error";
resultDiv.style.backgroundColor = "#dc3545"; /* Red for error */
resultCategoryDiv.innerHTML = "Please enter valid positive numbers for weight and height.";
resultCategoryDiv.style.color = "#dc3545";
return;
}
var heightM = heightCm / 100; // Convert height from cm to meters
var bmi = weightKg / (heightM * heightM);
var bmiRounded = bmi.toFixed(1); // Round BMI to one decimal place
var category = "";
var resultColor = "";
if (bmi = 18.5 && bmi = 25 && bmi = 30 && bmi = 35 && bmi <= 39.9) {
category = "Obesity Class II";
resultColor = "#dc3545"; /* Danger Red */
} else {
category = "Obesity Class III";
resultColor = "#dc3545"; /* Danger Red */
}
resultDiv.innerHTML = bmiRounded;
resultDiv.style.backgroundColor = resultColor;
resultCategoryDiv.innerHTML = category;
resultCategoryDiv.style.color = resultColor; /* Match text color to result background */
}