Body Fat Percentage Calculator
Estimate your body fat percentage using the US Navy Body Fat Formula. This method relies on specific body measurements to provide an approximation of your body composition.
Understanding Body Fat Percentage
Body fat percentage is a measure of how much of your total body weight is made up of fat. It's a more accurate indicator of fitness and health than just body weight or Body Mass Index (BMI), as it distinguishes between fat mass and lean mass (muscle, bone, water).
Why is Body Fat Percentage Important?
- Health Risk Assessment: High body fat percentages are associated with increased risks of chronic diseases like heart disease, type 2 diabetes, high blood pressure, and certain cancers.
- Fitness Goals: Athletes and fitness enthusiasts often monitor body fat to optimize performance and aesthetics. Lower body fat can improve athletic performance, while excessively low levels can be detrimental.
- Body Composition Insight: It provides a clearer picture of your body composition, helping you understand if changes in weight are due to fat loss/gain or muscle loss/gain.
How is Body Fat Percentage Calculated?
There are various methods to estimate body fat percentage, ranging from highly accurate lab tests to simpler field methods. This calculator uses a modified version of the US Navy Body Fat Formula, which is a widely used and relatively accessible method. It relies on specific circumference measurements:
- For Men: Height, Neck Circumference, and Waist Circumference.
- For Women: Height, Neck Circumference, Waist Circumference, and Hip Circumference.
These measurements are plugged into a logarithmic equation to estimate body fat percentage. While convenient, it's important to remember that this is an estimation and can have a margin of error.
Interpreting Your Results
Body fat percentage ranges vary based on age, gender, and fitness level. Here are general guidelines:
For Men:
- Essential Fat: 2-5% (Minimum fat required for physiological function)
- Athletes: 6-13% (Lean, highly conditioned individuals)
- Fitness: 14-17% (Good general fitness)
- Acceptable: 18-24% (Average, healthy range)
- Obese: 25% and above (Increased health risks)
For Women:
- Essential Fat: 10-13% (Minimum fat required for physiological function, including reproductive health)
- Athletes: 14-20% (Lean, highly conditioned individuals)
- Fitness: 21-24% (Good general fitness)
- Acceptable: 25-31% (Average, healthy range)
- Obese: 32% and above (Increased health risks)
Note: These ranges are general and can vary slightly depending on the source and individual factors. Consult with a healthcare professional or certified fitness expert for personalized advice.
Limitations of This Calculator
- Estimation: This calculator provides an estimate. Factors like measurement accuracy, body type, and hydration levels can influence the result.
- Formula Specificity: The US Navy formula is one of many. Other methods (e.g., DEXA scan, bioelectrical impedance, skinfold calipers) may yield different results.
- Not for Medical Diagnosis: This tool is for informational purposes only and should not be used to diagnose or treat any medical condition.
.fat-index-calculator-container {
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
max-width: 700px;
margin: 20px auto;
padding: 25px;
background-color: #f9f9f9;
border-radius: 10px;
box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
color: #333;
}
.fat-index-calculator-container h2 {
text-align: center;
color: #2c3e50;
margin-bottom: 20px;
font-size: 1.8em;
}
.fat-index-calculator-container p {
line-height: 1.6;
margin-bottom: 15px;
}
.calculator-form .form-group {
margin-bottom: 15px;
display: flex;
flex-wrap: wrap;
align-items: center;
}
.calculator-form label {
flex: 1;
min-width: 150px;
margin-right: 10px;
font-weight: bold;
color: #555;
}
.calculator-form input[type="number"],
.calculator-form select {
flex: 2;
padding: 10px;
border: 1px solid #ccc;
border-radius: 5px;
font-size: 1em;
max-width: 250px;
}
.calculator-form input[type="radio"] {
margin-right: 5px;
margin-left: 15px;
}
.calculator-form input[type="radio"] + label {
font-weight: normal;
min-width: unset;
flex: unset;
margin-right: 15px;
}
.calculator-form button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #28a745;
color: white;
border: none;
border-radius: 5px;
font-size: 1.1em;
cursor: pointer;
transition: background-color 0.3s ease;
margin-top: 20px;
}
.calculator-form button:hover {
background-color: #218838;
}
.calculator-result {
margin-top: 30px;
padding: 20px;
background-color: #e9f7ef;
border: 1px solid #d4edda;
border-radius: 8px;
font-size: 1.1em;
color: #155724;
text-align: center;
min-height: 50px;
display: flex;
align-items: center;
justify-content: center;
font-weight: bold;
}
.calculator-result.error {
background-color: #f8d7da;
border-color: #f5c6cb;
color: #721c24;
}
.calculator-info {
margin-top: 40px;
padding-top: 20px;
border-top: 1px solid #eee;
}
.calculator-info h3 {
color: #2c3e50;
margin-top: 25px;
margin-bottom: 15px;
font-size: 1.4em;
}
.calculator-info ul {
list-style-type: disc;
margin-left: 20px;
margin-bottom: 15px;
}
.calculator-info li {
margin-bottom: 8px;
line-height: 1.5;
}
@media (max-width: 600px) {
.calculator-form label {
min-width: 100%;
margin-bottom: 5px;
}
.calculator-form input[type="number"],
.calculator-form select {
max-width: 100%;
}
.calculator-form .form-group {
flex-direction: column;
align-items: flex-start;
}
}
function updateInputLabels() {
var unitSystem = document.querySelector('input[name="unitSystem"]:checked').value;
var heightLabel = document.getElementById('heightLabel');
var weightLabel = document.getElementById('weightLabel');
var neckLabel = document.getElementById('neckLabel');
var waistLabel = document.getElementById('waistLabel');
var hipLabel = document.getElementById('hipLabel');
if (unitSystem === 'metric') {
heightLabel.textContent = 'Height (cm):';
weightLabel.textContent = 'Weight (kg):';
neckLabel.textContent = 'Neck Circumference (cm):';
waistLabel.textContent = 'Waist Circumference (cm):';
hipLabel.textContent = 'Hip Circumference (cm):';
document.getElementById('height').placeholder = 'e.g., 175';
document.getElementById('weight').placeholder = 'e.g., 70';
document.getElementById('neckCircumference').placeholder = 'e.g., 38';
document.getElementById('waistCircumference').placeholder = 'e.g., 80';
document.getElementById('hipCircumference').placeholder = 'e.g., 95';
} else {
heightLabel.textContent = 'Height (inches):';
weightLabel.textContent = 'Weight (lbs):';
neckLabel.textContent = 'Neck Circumference (inches):';
waistLabel.textContent = 'Waist Circumference (inches):';
hipLabel.textContent = 'Hip Circumference (inches):';
document.getElementById('height').placeholder = 'e.g., 69';
document.getElementById('weight').placeholder = 'e.g., 155';
document.getElementById('neckCircumference').placeholder = 'e.g., 15';
document.getElementById('waistCircumference').placeholder = 'e.g., 32';
document.getElementById('hipCircumference').placeholder = 'e.g., 38';
}
}
function updateInputs() {
var gender = document.querySelector('input[name="gender"]:checked').value;
var hipGroup = document.getElementById('hipGroup');
if (gender === 'male') {
hipGroup.style.display = 'none';
document.getElementById('hipCircumference').value = "; // Clear hip value for male
} else {
hipGroup.style.display = 'flex';
}
updateInputLabels(); // Also update labels in case units changed
}
function calculateBodyFat() {
var gender = document.querySelector('input[name="gender"]:checked').value;
var unitSystem = document.querySelector('input[name="unitSystem"]:checked').value;
var heightInput = parseFloat(document.getElementById('height').value);
var neckInput = parseFloat(document.getElementById('neckCircumference').value);
var waistInput = parseFloat(document.getElementById('waistCircumference').value);
var hipInput = parseFloat(document.getElementById('hipCircumference').value); // Only used for women
var resultDiv = document.getElementById('result');
resultDiv.className = 'calculator-result'; // Reset class
// Input validation
if (isNaN(heightInput) || heightInput <= 0 ||
isNaN(neckInput) || neckInput <= 0 ||
isNaN(waistInput) || waistInput <= 0) {
resultDiv.innerHTML = 'Please enter valid positive numbers for all required measurements.';
resultDiv.classList.add('error');
return;
}
if (gender === 'female' && (isNaN(hipInput) || hipInput <= 0)) {
resultDiv.innerHTML = 'Please enter a valid positive number for Hip Circumference for females.';
resultDiv.classList.add('error');
return;
}
var height_in, neck_in, waist_in, hip_in;
// Convert all measurements to inches for calculation
if (unitSystem === 'metric') {
height_in = heightInput / 2.54;
neck_in = neckInput / 2.54;
waist_in = waistInput / 2.54;
hip_in = hipInput / 2.54;
} else { // Imperial
height_in = heightInput;
neck_in = neckInput;
waist_in = waistInput;
hip_in = hipInput;
}
var bodyFatPercentage;
if (gender === 'male') {
var logTerm1 = Math.log10(waist_in – neck_in);
var logTerm2 = Math.log10(height_in);
if (isNaN(logTerm1) || (waist_in – neck_in) <= 0) {
resultDiv.innerHTML = 'Error: Waist circumference must be greater than neck circumference for men.';
resultDiv.classList.add('error');
return;
}
if (isNaN(logTerm2) || height_in <= 0) {
resultDiv.innerHTML = 'Error: Invalid height measurement.';
resultDiv.classList.add('error');
return;
}
// US Navy Formula for Men
bodyFatPercentage = 86.010 * logTerm1 – 70.041 * logTerm2 + 36.76;
} else { // Female
var logTerm1 = Math.log10(waist_in + hip_in – neck_in);
var logTerm2 = Math.log10(height_in);
if (isNaN(logTerm1) || (waist_in + hip_in – neck_in) <= 0) {
resultDiv.innerHTML = 'Error: Sum of waist and hip circumference must be greater than neck circumference for women.';
resultDiv.classList.add('error');
return;
}
if (isNaN(logTerm2) || height_in <= 0) {
resultDiv.innerHTML = 'Error: Invalid height measurement.';
resultDiv.classList.add('error');
return;
}
// US Navy Formula for Women
bodyFatPercentage = 163.205 * logTerm1 – 97.684 * logTerm2 – 78.387;
}
if (isNaN(bodyFatPercentage) || bodyFatPercentage < 0) {
resultDiv.innerHTML = 'Could not calculate body fat percentage. Please check your measurements. Results might be negative due to unusual body proportions.';
resultDiv.classList.add('error');
return;
}
var category = '';
if (gender === 'male') {
if (bodyFatPercentage <= 5) category = 'Essential Fat';
else if (bodyFatPercentage <= 13) category = 'Athletes';
else if (bodyFatPercentage <= 17) category = 'Fitness';
else if (bodyFatPercentage <= 24) category = 'Acceptable';
else category = 'Obese';
} else { // Female
if (bodyFatPercentage <= 13) category = 'Essential Fat';
else if (bodyFatPercentage <= 20) category = 'Athletes';
else if (bodyFatPercentage <= 24) category = 'Fitness';
else if (bodyFatPercentage <= 31) category = 'Acceptable';
else category = 'Obese';
}
resultDiv.innerHTML = 'Your estimated Body Fat Percentage:
' + bodyFatPercentage.toFixed(2) + '%Category:
' + category + '';
}
// Initialize inputs on page load
document.addEventListener('DOMContentLoaded', function() {
updateInputs();
});