The Body Mass Index (BMI) is a numerical index that assesses the relationship between your weight and height. It's a widely used screening tool for categorizing weight status and is a key indicator for potential health risks associated with being underweight, normal weight, overweight, or obese.
How BMI is Calculated (Kilograms)
The formula for calculating BMI using weight in kilograms (kg) and height in centimeters (cm) is:
BMI = (Weight in kg / (Height in cm / 100)^2)
In simpler terms, you divide your weight in kilograms by your height in meters squared. Since the input is in centimeters, we first convert height to meters by dividing by 100.
BMI Categories:
Underweight: BMI less than 18.5
Normal weight: BMI between 18.5 and 24.9
Overweight: BMI between 25 and 29.9
Obesity: BMI 30 or greater
Why is BMI Important?
While BMI is not a direct measure of body fat, it is strongly correlated with it. A high BMI can indicate a higher proportion of body fat, which is associated with an increased risk of several chronic health conditions, including:
Heart disease and stroke
Type 2 diabetes
High blood pressure
Certain types of cancer
Osteoarthritis
Sleep apnea
Conversely, a BMI that is too low can also indicate potential health issues, such as malnutrition, osteoporosis, and nutrient deficiencies.
Limitations of BMI
It's important to remember that BMI is a screening tool and doesn't diagnose body fatness or health. Factors such as muscle mass, bone density, and body composition can influence BMI. For example, very muscular individuals may have a high BMI without having excess body fat. Therefore, it's always best to consult with a healthcare professional for a comprehensive health assessment.
Example Calculation:
Let's say an individual weighs 75 kg and is 180 cm tall.
Convert height to meters: 180 cm / 100 = 1.8 meters
Calculate height squared: 1.8 m * 1.8 m = 3.24 m²
Calculate BMI: 75 kg / 3.24 m² ≈ 23.15
A BMI of 23.15 falls into the "Normal weight" category.
function calculateBMI() {
var weightKgInput = document.getElementById("weightKg");
var heightCmInput = document.getElementById("heightCm");
var resultDiv = document.getElementById("result");
var weightKg = parseFloat(weightKgInput.value);
var heightCm = parseFloat(heightCmInput.value);
// Clear previous error messages or results
resultDiv.style.display = 'none';
resultDiv.innerHTML = ";
// Input validation
if (isNaN(weightKg) || weightKg <= 0) {
resultDiv.innerHTML = 'Please enter a valid weight in kilograms (must be a positive number).';
resultDiv.style.display = 'block';
resultDiv.style.borderColor = '#f5c6cb'; // Light red border
resultDiv.style.backgroundColor = '#f8d7da'; // Light red background
resultDiv.style.color = '#721c24'; // Dark red text
return;
}
if (isNaN(heightCm) || heightCm <= 0) {
resultDiv.innerHTML = 'Please enter a valid height in centimeters (must be a positive number).';
resultDiv.style.display = 'block';
resultDiv.style.borderColor = '#f5c6cb'; // Light red border
resultDiv.style.backgroundColor = '#f8d7da'; // Light red background
resultDiv.style.color = '#721c24'; // Dark red text
return;
}
// Convert height from cm to meters
var heightM = heightCm / 100;
// Calculate BMI
var bmi = weightKg / (heightM * heightM);
var bmiRounded = bmi.toFixed(2); // Round to 2 decimal places
var category = "";
var resultHtml = '' + bmiRounded + '';
// Determine BMI category
if (bmi = 18.5 && bmi = 25 && bmi = 30
category = "Obesity";
resultHtml += 'Category: Obesity';
resultDiv.style.borderColor = '#f5c6cb'; // Light red border
resultDiv.style.backgroundColor = '#f8d7da'; // Light red background
resultDiv.style.color = '#721c24'; // Dark red text
}
resultDiv.innerHTML = resultHtml;
resultDiv.style.display = 'block';
}