Calculate your Body Mass Index using kilograms for weight and centimeters for height.
Your BMI Results
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What is Body Mass Index (BMI)?
Body Mass Index (BMI) is a simple, non-invasive tool used to estimate body fat and categorize a person's weight status relative to their height. It's calculated using a formula that takes into account both your weight and your height. While BMI doesn't directly measure body fat, it serves as a widely accepted screening tool for identifying weight categories that may lead to health problems.
The BMI Formula Explained
The standard formula for calculating BMI using metric units is:
BMI = Weight (kg) / (Height (m))^2
In this calculator, we ask for height in centimeters (cm) for user convenience. To use the formula, height must be converted to meters (m) by dividing the centimeter value by 100. So, if your height is 175 cm, it becomes 1.75 m.
For example: If a person weighs 70 kg and is 175 cm tall (1.75 m):
BMI = 70 kg / (1.75 m * 1.75 m) = 70 / 3.0625 = 22.86
The resulting BMI value is then compared against standard BMI ranges to determine the weight category.
BMI Weight Categories
The World Health Organization (WHO) and other health organizations use the following standard BMI categories:
Underweight: Less than 18.5
Normal weight: 18.5 – 24.9
Overweight: 25 – 29.9
Obesity (Class I): 30 – 34.9
Obesity (Class II): 35 – 39.9
Obesity (Class III): 40 or greater
Why Use a BMI Calculator?
Health Screening: BMI is an initial screening tool to identify potential weight-related health risks.
Weight Management: It can help individuals and healthcare providers track weight status and set health goals.
Simplicity: The calculation is straightforward and requires only two readily available measurements.
Accessibility: Online calculators make it easy for anyone to compute their BMI quickly and privately.
Important Considerations
BMI is a useful tool, but it has limitations. It does not differentiate between muscle mass and fat mass, so individuals with high muscle mass (like athletes) may have a high BMI without being unhealthy. Similarly, it doesn't account for body composition, fat distribution, or age. It's always recommended to consult with a healthcare professional for a comprehensive assessment of your health and weight status.
function calculateBMI() {
var weightKg = document.getElementById("weightKg").value;
var heightCm = document.getElementById("heightCm").value;
var bmiValueElement = document.getElementById("bmiValue");
var bmiCategoryElement = document.getElementById("bmiCategory");
// Clear previous results
bmiValueElement.innerText = "–";
bmiCategoryElement.innerText = "";
// Validate inputs
if (weightKg === "" || heightCm === "" || isNaN(weightKg) || isNaN(heightCm)) {
bmiCategoryElement.innerText = "Please enter valid numbers for weight and height.";
return;
}
var weight = parseFloat(weightKg);
var height = parseFloat(heightCm);
if (weight <= 0 || height <= 0) {
bmiCategoryElement.innerText = "Weight and height must be positive values.";
return;
}
// Convert height from cm to meters
var heightM = height / 100;
// Calculate BMI
var bmi = weight / (heightM * heightM);
bmi = bmi.toFixed(1); // Round to one decimal place
bmiValueElement.innerText = bmi;
// Determine BMI category
var category = "";
if (bmi = 18.5 && bmi = 25 && bmi = 30 && bmi = 35 && bmi = 40
category = "Obesity (Class III)";
bmiCategoryElement.style.color = "#dc3545"; // Danger red
}
bmiCategoryElement.innerText = category;
}