Calculate your Body Mass Index (BMI) using your weight and height.
Your BMI
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Understanding Your BMI
Body Mass Index (BMI) is a measure that uses your weight and height to estimate the amount of body fat a person has. It's a common screening tool used to categorize a person's weight status relative to their height, and to help identify potential weight-related health risks. The BMI formula is a simple calculation, making it accessible and widely used by healthcare professionals.
The BMI Formula
The standard formula for calculating BMI is:
BMI = weight (kg) / (height (m))^2
Where:
Weight is measured in kilograms (kg).
Height is measured in meters (m).
In this calculator, we ask for height in centimeters (cm) for user convenience. The calculator automatically converts centimeters to meters (1 meter = 100 centimeters) before applying the formula. So, if you enter 175 cm for height, it's used as 1.75 meters in the calculation.
Interpreting Your BMI Score
The calculated BMI score is then compared against a standard classification developed by organizations like the World Health Organization (WHO). These categories help provide context for the BMI number:
Underweight: BMI less than 18.5
Healthy weight: BMI 18.5 to 24.9
Overweight: BMI 25.0 to 29.9
Obese: BMI 30.0 or greater
It's important to note that BMI is a screening tool and does not diagnose body fatness or health. Factors like muscle mass, bone density, and distribution of fat can influence health outcomes and may not be fully captured by BMI alone. For a comprehensive health assessment, it's always recommended to consult with a healthcare professional.
When to Use a BMI Calculator
A BMI calculator is useful for:
Gaining a general understanding of your current weight status.
Tracking changes in your weight status over time.
Identifying if you might be at increased risk for certain health conditions associated with being underweight, overweight, or obese.
Setting realistic health and fitness goals.
This tool is a starting point for understanding your relationship with your weight and can be a valuable part of a broader health journey.
function calculateBMI() {
var weightInput = document.getElementById("weight");
var heightInput = document.getElementById("height");
var bmiValueElement = document.getElementById("bmiValue");
var bmiCategoryElement = document.getElementById("bmiCategory");
var weight = parseFloat(weightInput.value);
var heightCm = parseFloat(heightInput.value);
// Clear previous results and error messages
bmiValueElement.textContent = "–";
bmiCategoryElement.textContent = "–";
bmiCategoryElement.className = "bmi-category"; // Reset classes
// Input validation
if (isNaN(weight) || isNaN(heightCm) || weight <= 0 || heightCm <= 0) {
bmiCategoryElement.textContent = "Please enter valid positive numbers for weight and height.";
bmiCategoryElement.className += " error"; // You might want to style an error class
return;
}
// Convert height from cm to meters
var heightM = heightCm / 100;
// Calculate BMI
var bmi = weight / (heightM * heightM);
// Display BMI value, rounded to two decimal places
bmiValueElement.textContent = bmi.toFixed(2);
// Determine BMI category and apply appropriate styling
var category = "";
if (bmi = 18.5 && bmi = 25 && bmi = 30) {
category = "Obese";
bmiCategoryElement.className += " bmi-category obese";
}
bmiCategoryElement.textContent = category;
}