Lean Body Mass (LBM) is a critical health metric that represents the total weight of your body minus all the weight from your fat mass. Essentially, it includes the weight of your organs, skin, bones, water, and most importantly, your muscles.
Why is Lean Body Mass Important?
Unlike Body Mass Index (BMI), which only looks at weight and height, LBM provides insight into your body composition. Athletes and fitness enthusiasts track LBM to ensure that their weight loss is coming from fat rather than muscle. A higher LBM is generally associated with a higher Basal Metabolic Rate (BMR), meaning your body burns more calories at rest.
The Calculation Formula
This calculator utilizes the Boer Formula, which is widely recognized as one of the most accurate mathematical estimations for lean body mass:
For Men: LBM = (0.407 × weight in kg) + (0.267 × height in cm) – 19.2
For Women: LBM = (0.252 × weight in kg) + (0.473 × height in cm) – 48.3
Practical Example
Imagine a male individual who weighs 85 kg and stands 180 cm tall:
LBM = (0.407 × 85) + (0.267 × 180) – 19.2
LBM = 34.595 + 48.06 – 19.2 Result: 63.45 kg of Lean Body Mass
This means that out of his total 85 kg weight, approximately 63.45 kg is bone, muscle, and water, while the remaining 21.55 kg is fat (approx. 25% body fat).
Tips to Improve Lean Body Mass
Resistance Training: Lifting weights is the most effective way to build and preserve muscle tissue.
Protein Intake: Consume adequate protein (typically 1.6g to 2.2g per kg of body weight) to repair muscle fibers.
Hydration: Since muscle is roughly 75% water, staying hydrated is essential for maintaining lean mass.
Rest: Muscles grow during rest periods, not during the actual workout.
function toggleLbmUnits() {
var unit = document.getElementById('lbmUnit').value;
var weightLabel = document.getElementById('weightLabel');
var heightLabel = document.getElementById('heightLabel');
if (unit === 'metric') {
weightLabel.innerHTML = 'Weight (kg)';
heightLabel.innerHTML = 'Height (cm)';
} else {
weightLabel.innerHTML = 'Weight (lbs)';
heightLabel.innerHTML = 'Height (inches)';
}
}
function calculateLBM() {
var gender = document.getElementById('lbmGender').value;
var unit = document.getElementById('lbmUnit').value;
var weight = parseFloat(document.getElementById('lbmWeight').value);
var height = parseFloat(document.getElementById('lbmHeight').value);
var resultDiv = document.getElementById('lbmResultContainer');
var lbmValueDisp = document.getElementById('lbmValue');
var lbmFatFreeDisp = document.getElementById('lbmFatFree');
var lbmFatMassDisp = document.getElementById('lbmFatMass');
if (isNaN(weight) || isNaN(height) || weight <= 0 || height <= 0) {
alert("Please enter valid positive numbers for weight and height.");
return;
}
var weightKg = weight;
var heightCm = height;
// Convert to metric for calculation if imperial is selected
if (unit === 'imperial') {
weightKg = weight * 0.453592;
heightCm = height * 2.54;
}
var lbm = 0;
if (gender === 'male') {
// Boer Formula for Men
lbm = (0.407 * weightKg) + (0.267 * heightCm) – 19.2;
} else {
// Boer Formula for Women
lbm = (0.252 * weightKg) + (0.473 * heightCm) – 48.3;
}
// Safety check for unrealistic results
if (lbm weightKg) lbm = weightKg;
var fatMassKg = weightKg – lbm;
var bodyFatPercentage = (fatMassKg / weightKg) * 100;
var displayLbm, displayUnit;
if (unit === 'metric') {
displayLbm = lbm.toFixed(2);
displayUnit = "kg";
} else {
displayLbm = (lbm * 2.20462).toFixed(2);
displayUnit = "lbs";
}
lbmValueDisp.innerHTML = displayLbm + " " + displayUnit;
lbmFatFreeDisp.innerHTML = "Your body is approximately " + (100 – bodyFatPercentage).toFixed(1) + "% lean tissue.";
lbmFatMassDisp.innerHTML = "Estimated Body Fat: " + bodyFatPercentage.toFixed(1) + "%";
resultDiv.style.display = "block";
resultDiv.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}