Body Mass Index (BMI) is a simple and widely used tool to estimate whether an individual is at a healthy weight for their height. It's a screening tool, not a diagnostic tool, and should be interpreted by a healthcare professional. BMI helps categorize weight into different ranges, which can indicate potential health risks associated with being underweight, overweight, or obese.
How BMI is Calculated
The formula for BMI is straightforward, requiring only two measurements: your weight and your height. The standard formula is:
BMI = Weight (kg) / (Height (m))2
In this calculator, we use metric units. If your height is in centimeters (cm), you first need to convert it to meters (m) by dividing by 100. For example, 175 cm becomes 1.75 m.
BMI Categories
The calculated BMI value is then compared against a standard range to determine your weight category. These categories are generally defined as follows:
Underweight: BMI less than 18.5
Normal weight: BMI between 18.5 and 24.9
Overweight: BMI between 25 and 29.9
Obese: BMI of 30 or greater
It's important to remember that BMI has limitations. It does not distinguish between muscle mass and fat mass, so a very muscular person might have a high BMI but still be healthy. Similarly, it doesn't account for body fat distribution or age-specific norms. Always consult with a doctor or a registered dietitian for personalized health advice.
When to Use a BMI Calculator
A BMI calculator is useful for:
Gaining a quick estimate of your weight status.
Tracking changes in your weight over time in relation to your height.
Understanding potential health risks associated with your current weight.
Setting realistic weight management goals.
This tool is designed to be informative and easy to use. Simply input your weight in kilograms and your height in centimeters to get your BMI and its corresponding category.
function calculateBMI() {
var weight = document.getElementById("weight").value;
var heightCm = document.getElementById("height").value;
var resultDiv = document.getElementById("result");
// Clear previous classes
resultDiv.className = "";
// Input validation
if (weight === "" || heightCm === "" || isNaN(weight) || isNaN(heightCm) || weight <= 0 || heightCm <= 0) {
resultDiv.innerHTML = "Please enter valid numbers for weight and height.";
return;
}
var heightM = heightCm / 100; // Convert height from cm to meters
var bmi = weight / (heightM * heightM);
// Round BMI to two decimal places
bmi = bmi.toFixed(2);
var bmiCategory = "";
var resultText = "Your BMI is: " + bmi + " (";
if (bmi = 18.5 && bmi = 25 && bmi = 30
bmiCategory = "obese";
resultText += "Obese)";
resultDiv.classList.add("obese");
}
resultDiv.innerHTML = resultText;
resultDiv.setAttribute("data-category", bmiCategory); // Optional: add data attribute for styling/scripting
}