Body Mass Index (BMI) is a simple calculation used to estimate whether your weight is healthy for your height. It's a widely used screening tool, but it doesn't account for body composition (muscle vs. fat). Muscle mass is a crucial component of overall health and fitness. This calculator provides both your BMI and an estimate of your muscle mass, giving you a more comprehensive picture of your health.
How BMI is Calculated:
BMI is calculated using the following formula:
Metric Units: BMI = Weight (kg) / (Height (m))^2
For easier input, we use Height in centimeters (cm) and convert it to meters (m) within the calculation: Height (m) = Height (cm) / 100
BMI Categories:
Underweight: Below 18.5
Healthy Weight: 18.5 – 24.9
Overweight: 25 – 29.9
Obese: 30 and above
Estimating Muscle Mass:
To estimate muscle mass, we first calculate your fat mass and lean body mass. Lean body mass includes everything in your body that isn't fat: organs, bones, muscles, water, etc. Since muscle is a significant component of lean body mass, this provides a good proxy.
While this calculator estimates Lean Body Mass, it's important to note that dedicated methods like DEXA scans or bioelectrical impedance analysis (BIA) offer more precise body composition measurements.
Disclaimer: This calculator is for informational purposes only and should not be considered medical advice. Consult with a healthcare professional for personalized health and fitness guidance.
function calculateBMIandMuscleMass() {
var weightKg = parseFloat(document.getElementById("weight").value);
var heightCm = parseFloat(document.getElementById("height").value);
var bodyFatPercentage = parseFloat(document.getElementById("bodyFatPercentage").value);
var bmiResult = document.getElementById("result-value");
var bmiCategoryDisplay = document.getElementById("bmi-category");
var leanMassDisplay = document.getElementById("lean-mass-display");
var fatMassDisplay = document.getElementById("fat-mass-display");
// Clear previous results and styles
bmiResult.innerHTML = "–";
bmiCategoryDisplay.innerHTML = "–";
leanMassDisplay.innerHTML = "–";
fatMassDisplay.innerHTML = "–";
bmiResult.style.color = "#28a745"; // Default to success green
// Validate inputs
if (isNaN(weightKg) || isNaN(heightCm) || isNaN(bodyFatPercentage) || weightKg <= 0 || heightCm <= 0 || bodyFatPercentage 100) {
alert("Please enter valid numbers for weight, height, and body fat percentage.");
return;
}
// Calculate BMI
var heightM = heightCm / 100;
var bmi = weightKg / (heightM * heightM);
bmi = bmi.toFixed(1); // Round BMI to one decimal place
// Determine BMI Category
var bmiCategory;
if (bmi = 18.5 && bmi = 25 && bmi <= 29.9) {
bmiCategory = "Overweight";
bmiResult.style.color = "#fd7e14"; // Orange
} else {
bmiCategory = "Obese";
bmiResult.style.color = "#dc3545"; // Danger red
}
// Calculate Fat Mass and Lean Body Mass
var fatMassKg = weightKg * (bodyFatPercentage / 100);
var leanMassKg = weightKg – fatMassKg;
// Display results
bmiResult.innerHTML = bmi + " kg/m²";
bmiCategoryDisplay.innerHTML = "BMI Category: " + bmiCategory;
fatMassDisplay.innerHTML = "Estimated Fat Mass: " + fatMassKg.toFixed(1) + " kg";
leanMassDisplay.innerHTML = "Estimated Lean Body Mass: " + leanMassKg.toFixed(1) + " kg";
}