Body Composition Calculator
Use this calculator to estimate your Body Mass Index (BMI), Body Fat Percentage, and Lean Body Mass. These metrics can provide insights into your overall health and fitness level.
Understanding Body Composition
Body composition refers to the proportion of fat and non-fat mass in your body. A healthy body composition typically involves a lower percentage of body fat and a higher percentage of lean body mass (muscle, bone, and organs). It's a more comprehensive indicator of health than just body weight alone, as two people of the same weight and height can have very different body compositions and health risks.
Key Metrics Explained
Body Mass Index (BMI)
BMI is a simple index of weight-for-height that is commonly used to classify underweight, overweight, and obesity in adults. It is defined as the weight in kilograms divided by the square of the height in meters (kg/m²).
- Underweight: BMI less than 18.5
- Normal weight: BMI 18.5 to 24.9
- Overweight: BMI 25.0 to 29.9
- Obesity: BMI 30.0 or greater
While useful for population studies, BMI has limitations for individuals as it doesn't distinguish between muscle and fat mass. A very muscular person might have a high BMI but a healthy body fat percentage.
Body Fat Percentage
Body fat percentage is the total mass of fat divided by total body mass, multiplied by 100. It's a more direct measure of body fatness than BMI. The calculator uses a modified version of the U.S. Navy Body Fat Calculator method, which relies on circumference measurements.
General Body Fat Percentage Categories:
- Essential Fat: Men: 2-5%, Women: 10-13%
- Athletes: Men: 6-13%, Women: 14-20%
- Fitness: Men: 14-17%, Women: 21-24%
- Acceptable: Men: 18-24%, Women: 25-31%
- Obese: Men: 25%+ , Women: 32%+
These ranges can vary slightly based on age and individual differences. Essential fat is necessary for life and reproductive functions.
Lean Body Mass (LBM)
Lean Body Mass is the total weight of your body minus all the fat mass. It includes the weight of your organs, skin, bones, and muscle mass. LBM is important for metabolic rate and overall strength. A higher LBM generally indicates a healthier body composition.
How to Use the Calculator
- Select Unit System: Choose between Metric (cm, kg) or Imperial (inches, lbs).
- Select Gender: This is crucial as body fat formulas differ for men and women.
- Enter Age: While not directly used in the US Navy body fat formula, age is a factor in overall health assessment.
- Enter Measurements:
- Height: Stand tall and measure from the top of your head to the floor.
- Weight: Use a reliable scale, preferably in the morning before eating.
- Neck Circumference: Measure just below the larynx (Adam's apple), keeping the tape parallel to the floor.
- Waist Circumference: For men, measure at the navel. For women, measure at the narrowest point of the waist.
- Hip Circumference (Women Only): Measure at the widest part of the hips.
- Click "Calculate": Your estimated BMI, Body Fat Percentage, and Lean Body Mass will be displayed.
Important Considerations
This calculator provides estimates based on widely used formulas. Circumference-based methods for body fat percentage can have a margin of error and may not be as accurate as clinical methods like DEXA scans or hydrostatic weighing. Factors like hydration levels, recent meals, and measurement technique can influence results.
Always consult with a healthcare professional or a certified fitness expert for personalized advice regarding your body composition and health goals.
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.calc-results .bmi-category, .calc-results .bf-category {
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padding: 3px 8px;
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.bmi-underweight { background-color: #ffeb3b; color: #333; } /* Yellow */
.bmi-normal { background-color: #8bc34a; color: white; } /* Green */
.bmi-overweight { background-color: #ff9800; color: white; } /* Orange */
.bmi-obese { background-color: #f44336; color: white; } /* Red */
.bf-essential { background-color: #add8e6; color: #333; } /* Light Blue */
.bf-athlete { background-color: #8bc34a; color: white; } /* Green */
.bf-fitness { background-color: #ffeb3b; color: #333; } /* Yellow */
.bf-acceptable { background-color: #ff9800; color: white; } /* Orange */
.bf-obese { background-color: #f44336; color: white; } /* Red */
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max-width: 100%;
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}
function updateUnitLabels() {
var unitSystem = document.querySelector('input[name="unitSystem"]:checked').value;
if (unitSystem === 'metric') {
document.getElementById('heightLabel').innerText = 'Height (cm):';
document.getElementById('weightLabel').innerText = 'Weight (kg):';
document.getElementById('neckLabel').innerText = 'Neck Circumference (cm):';
document.getElementById('waistLabel').innerText = 'Waist Circumference (cm):';
document.getElementById('hipLabel').innerText = 'Hip Circumference (cm):';
} else {
document.getElementById('heightLabel').innerText = 'Height (inches):';
document.getElementById('weightLabel').innerText = 'Weight (lbs):';
document.getElementById('neckLabel').innerText = 'Neck Circumference (inches):';
document.getElementById('waistLabel').innerText = 'Waist Circumference (inches):';
document.getElementById('hipLabel').innerText = 'Hip Circumference (inches):';
}
}
function toggleHipCircumference() {
var gender = document.querySelector('input[name="gender"]:checked').value;
var hipGroup = document.getElementById('hipGroup');
if (gender === 'female') {
hipGroup.style.display = 'flex';
} else {
hipGroup.style.display = 'none';
}
}
function getBMICategory(bmi) {
if (bmi < 18.5) return '
Underweight';
if (bmi >= 18.5 && bmi <= 24.9) return '
Normal weight';
if (bmi >= 25.0 && bmi <= 29.9) return '
Overweight';
return '
Obese';
}
function getBodyFatCategory(gender, age, bfp) {
var category = ";
var className = ";
if (gender === 'male') {
if (bfp <= 5) { className = 'bf-essential'; category = 'Essential Fat'; }
else if (bfp <= 13) { className = 'bf-athlete'; category = 'Athletes'; }
else if (bfp <= 17) { className = 'bf-fitness'; category = 'Fitness'; }
else if (bfp <= 24) { className = 'bf-acceptable'; category = 'Acceptable'; }
else { className = 'bf-obese'; category = 'Obese'; }
} else { // female
if (bfp <= 13) { className = 'bf-essential'; category = 'Essential Fat'; }
else if (bfp <= 20) { className = 'bf-athlete'; category = 'Athletes'; }
else if (bfp <= 24) { className = 'bf-fitness'; category = 'Fitness'; }
else if (bfp <= 31) { className = 'bf-acceptable'; category = 'Acceptable'; }
else { className = 'bf-obese'; category = 'Obese'; }
}
return '
' + category + '';
}
function calculateBodyComposition() {
var unitSystem = document.querySelector('input[name="unitSystem"]:checked').value;
var gender = document.querySelector('input[name="gender"]:checked').value;
var age = parseFloat(document.getElementById('age').value);
var heightInput = parseFloat(document.getElementById('heightInput').value);
var weightInput = parseFloat(document.getElementById('weightInput').value);
var neckCircumference = parseFloat(document.getElementById('neckCircumference').value);
var waistCircumference = parseFloat(document.getElementById('waistCircumference').value);
var hipCircumference = parseFloat(document.getElementById('hipCircumference').value);
var resultDiv = document.getElementById('result');
resultDiv.innerHTML = ";
// Input validation
if (isNaN(age) || age <= 0 ||
isNaN(heightInput) || heightInput <= 0 ||
isNaN(weightInput) || weightInput <= 0 ||
isNaN(neckCircumference) || neckCircumference <= 0 ||
isNaN(waistCircumference) || waistCircumference <= 0) {
resultDiv.innerHTML = 'Please enter valid positive numbers for all required fields.';
return;
}
if (gender === 'female' && (isNaN(hipCircumference) || hipCircumference <= 0)) {
resultDiv.innerHTML = 'Please enter a valid positive number for Hip Circumference for females.';
return;
}
// Convert all inputs to standard units for calculation
var heightCm, weightKg, neckCm, waistCm, hipCm;
var heightInches, weightLbs, neckInches, waistInches, hipInches;
if (unitSystem === 'metric') {
heightCm = heightInput;
weightKg = weightInput;
neckCm = neckCircumference;
waistCm = waistCircumference;
hipCm = hipCircumference;
heightInches = heightCm / 2.54;
weightLbs = weightKg / 0.453592;
neckInches = neckCm / 2.54;
waistInches = waistCm / 2.54;
hipInches = hipCm / 2.54;
} else { // imperial
heightInches = heightInput;
weightLbs = weightInput;
neckInches = neckCircumference;
waistInference = waistCircumference;
hipInches = hipCircumference;
heightCm = heightInches * 2.54;
weightKg = weightLbs * 0.453592;
neckCm = neckInches * 2.54;
waistCm = waistInches * 2.54;
hipCm = hipInches * 2.54;
}
// — BMI Calculation —
var heightMeters = heightCm / 100;
var bmi = weightKg / (heightMeters * heightMeters);
// — Body Fat Percentage (US Navy Method) —
var bodyFatPercentage;
if (gender === 'male') {
// Formula for men: 86.010 * log10(waist – neck) – 70.041 * log10(height) + 36.76
// Ensure (waistInches – neckInches) is positive
if (waistInches <= neckInches) {
resultDiv.innerHTML = 'For men, Waist Circumference must be greater than Neck Circumference for body fat calculation.';
return;
}
bodyFatPercentage = 86.010 * Math.log10(waistInches – neckInches) – 70.041 * Math.log10(heightInches) + 36.76;
} else { // female
// Formula for women: 163.205 * log10(waist + hip – neck) – 97.684 * log10(height) – 78.387
// Ensure (waistInches + hipInches – neckInches) is positive
if ((waistInches + hipInches) <= neckInches) {
resultDiv.innerHTML = 'For women, (Waist + Hip Circumference) must be greater than Neck Circumference for body fat calculation.';
return;
}
bodyFatPercentage = 163.205 * Math.log10(waistInches + hipInches – neckInches) – 97.684 * Math.log10(heightInches) – 78.387;
}
// Ensure body fat percentage is not negative or excessively high
bodyFatPercentage = Math.max(0, Math.min(100, bodyFatPercentage));
// — Lean Body Mass Calculation —
var leanBodyMassKg = weightKg * (1 – (bodyFatPercentage / 100));
var leanBodyMassLbs = weightLbs * (1 – (bodyFatPercentage / 100));
// Display results
var bmiCategory = getBMICategory(bmi);
var bfCategory = getBodyFatCategory(gender, age, bodyFatPercentage);
var output = '
Your Body Composition Results:
';
output += '
BMI: ' + bmi.toFixed(2) + ' ' + bmiCategory + ";
output += '
Body Fat Percentage: ' + bodyFatPercentage.toFixed(2) + '% ' + bfCategory + ";
output += '
Lean Body Mass: ' + leanBodyMassKg.toFixed(2) + ' kg (' + leanBodyMassLbs.toFixed(2) + ' lbs)';
output += '
Note: Body fat percentage is an estimate using the US Navy method.';
resultDiv.innerHTML = output;
}
// Initialize on page load
document.addEventListener('DOMContentLoaded', function() {
toggleHipCircumference(); // Set initial visibility for hip circumference
updateUnitLabels(); // Set initial unit labels
});