Estimate your body fat percentage using the U.S. Navy circumference method. Please enter your measurements in inches.
function toggleHipInput() {
var genderFemale = document.getElementById('genderFemale').checked;
var hipInputGroup = document.getElementById('hipInputGroup');
if (genderFemale) {
hipInputGroup.style.display = 'block';
} else {
hipInputGroup.style.display = 'none';
document.getElementById('hipCircumference').value = "; // Clear value when hidden
}
}
function calculateBFP() {
var genderMale = document.getElementById('genderMale').checked;
var genderFemale = document.getElementById('genderFemale').checked;
var height = parseFloat(document.getElementById('heightInches').value);
var neck = parseFloat(document.getElementById('neckCircumference').value);
var waist = parseFloat(document.getElementById('waistCircumference').value);
var hip = parseFloat(document.getElementById('hipCircumference').value);
var weight = parseFloat(document.getElementById('weightLbs').value);
var resultDiv = document.getElementById('bfpResult');
resultDiv.innerHTML = "; // Clear previous results
if (isNaN(height) || height <= 0 ||
isNaN(neck) || neck <= 0 ||
isNaN(waist) || waist <= 0 ||
isNaN(weight) || weight <= 0) {
resultDiv.innerHTML = 'Please enter valid positive numbers for all required fields.';
return;
}
if (genderFemale && (isNaN(hip) || hip <= 0)) {
resultDiv.innerHTML = 'Please enter a valid positive number for Hip Circumference for females.';
return;
}
var bfp = 0;
var log10 = function(val) {
return Math.log(val) / Math.log(10);
};
if (genderMale) {
var diff = waist – neck;
if (diff <= 0) {
resultDiv.innerHTML = 'Waist circumference must be greater than neck circumference for an accurate male calculation.';
return;
}
bfp = 86.010 * log10(diff) – 70.041 * log10(height) + 36.76;
} else { // Female
var sumDiff = waist + hip – neck;
if (sumDiff <= 0) {
resultDiv.innerHTML = 'The sum of waist and hip circumference must be greater than neck circumference for an accurate female calculation.';
return;
}
bfp = 163.205 * log10(sumDiff) – 97.684 * log10(height) – 78.387;
}
if (bfp < 0) bfp = 0; // Body fat cannot be negative
var bodyFatMass = (bfp / 100) * weight;
var leanBodyMass = weight – bodyFatMass;
var output = '
Body Fat Percentage (BFP) is a crucial metric that represents the total mass of fat divided by total body mass, multiplied by 100. Unlike Body Mass Index (BMI), which only considers height and weight, BFP provides a more accurate picture of body composition by distinguishing between fat mass and lean mass (muscle, bone, organs, water).
Why is BFP Important?
Health Indicator: Excess body fat, especially visceral fat around organs, is linked to various health issues like heart disease, type 2 diabetes, high blood pressure, and certain cancers. Too little body fat can also be detrimental, affecting hormone production and overall health.
Fitness Goals: For athletes and fitness enthusiasts, BFP helps track progress more effectively than just weight. Losing fat while maintaining or gaining muscle is a common goal, and BFP reflects this change.
Body Composition Assessment: It offers a better understanding of your physical makeup, guiding dietary and exercise strategies.
How is BFP Measured?
Several methods exist to estimate BFP, each with varying levels of accuracy and cost:
DEXA Scan (Dual-energy X-ray Absorptiometry): Considered one of the most accurate methods, it uses X-rays to differentiate between bone, lean tissue, and fat.
Hydrostatic Weighing (Underwater Weighing): Measures body density by submerging a person in water. More dense individuals (more muscle/bone) will weigh more underwater.
Bioelectrical Impedance Analysis (BIA): Sends a small electrical current through the body. Fat impedes the current more than lean tissue, allowing for an estimate. Accuracy can vary based on hydration levels.
Skinfold Calipers: Measures the thickness of subcutaneous fat at various sites on the body. Requires skill to perform accurately.
Circumference Method (U.S. Navy Method): This is the method used in the calculator above. It's a practical and accessible way to estimate BFP using simple tape measurements of specific body parts (neck, waist, hip, height). While not as precise as DEXA, it provides a reasonable estimate for tracking changes over time.
Interpreting Your BFP Results
Ideal body fat percentages vary based on age, gender, and activity level. Here are general guidelines:
For Men:
Essential Fat: 2-5% (Minimum required for physiological function)
Athletes: 6-13%
Fitness: 14-17%
Acceptable: 18-24%
Obese: 25% and above
For Women:
Essential Fat: 10-13% (Higher due to reproductive functions)
Athletes: 14-20%
Fitness: 21-24%
Acceptable: 25-31%
Obese: 32% and above
Remember, these are general guidelines. Individual health and fitness goals should always be considered. Consult with a healthcare professional or a certified fitness expert for personalized advice.
Limitations of the Calculator
The U.S. Navy circumference method is an estimation and may not be perfectly accurate for everyone. Factors like individual body shape, measurement technique, and ethnicity can influence the results. It's best used as a tool to track trends over time rather than a definitive, one-time measurement. For the most accurate assessment, consider professional methods like DEXA scans.