Enter your measurements and click 'Calculate' to see your body fat percentage.
function calculateBodyFat() {
var genderMale = document.getElementById('genderMale').checked;
var genderFemale = document.getElementById('genderFemale').checked;
var heightInches = parseFloat(document.getElementById('heightInches').value);
var neckCircumference = parseFloat(document.getElementById('neckCircumference').value);
var waistCircumference = parseFloat(document.getElementById('waistCircumference').value);
var hipCircumference = parseFloat(document.getElementById('hipCircumference').value); // Only used for females
var resultDiv = document.getElementById('bodyFatResult');
resultDiv.style.color = '#333'; // Reset color
if (isNaN(heightInches) || isNaN(neckCircumference) || isNaN(waistCircumference) ||
heightInches <= 0 || neckCircumference <= 0 || waistCircumference <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all required measurements.";
resultDiv.style.color = 'red';
return;
}
var bodyFatPercentage;
var category = "";
if (genderMale) {
var logWaistNeck = Math.log10(waistCircumference – neckCircumference);
if (isNaN(logWaistNeck) || (waistCircumference – neckCircumference) <= 0) {
resultDiv.innerHTML = "Error: Waist circumference must be greater than neck circumference for calculation.";
resultDiv.style.color = 'red';
return;
}
bodyFatPercentage = 86.010 * logWaistNeck – 70.041 * Math.log10(heightInches) + 36.76;
if (bodyFatPercentage 100) bodyFatPercentage = 100; // Cap at 100%
if (bodyFatPercentage <= 5) {
category = "Essential Fat";
} else if (bodyFatPercentage <= 13) {
category = "Athletes";
} else if (bodyFatPercentage <= 17) {
category = "Fitness";
} else if (bodyFatPercentage <= 24) {
category = "Average";
} else {
category = "Obese";
}
} else if (genderFemale) {
if (isNaN(hipCircumference) || hipCircumference <= 0) {
resultDiv.innerHTML = "Please enter a valid positive number for Hip Circumference for females.";
resultDiv.style.color = 'red';
return;
}
var logWaistHipNeck = Math.log10(waistCircumference + hipCircumference – neckCircumference);
if (isNaN(logWaistHipNeck) || (waistCircumference + hipCircumference – neckCircumference) <= 0) {
resultDiv.innerHTML = "Error: (Waist + Hip) circumference must be greater than neck circumference for calculation.";
resultDiv.style.color = 'red';
return;
}
bodyFatPercentage = 163.205 * logWaistHipNeck – 97.684 * Math.log10(heightInches) – 78.387;
if (bodyFatPercentage 100) bodyFatPercentage = 100; // Cap at 100%
if (bodyFatPercentage <= 13) {
category = "Essential Fat";
} else if (bodyFatPercentage <= 20) {
category = "Athletes";
} else if (bodyFatPercentage <= 24) {
category = "Fitness";
} else if (bodyFatPercentage <= 31) {
category = "Average";
} else {
category = "Obese";
}
}
if (isNaN(bodyFatPercentage)) {
resultDiv.innerHTML = "Could not calculate body fat percentage. Please check your inputs.";
resultDiv.style.color = 'red';
} else {
resultDiv.innerHTML = "Your estimated Body Fat Percentage: " + bodyFatPercentage.toFixed(2) + "%Category: " + category + "";
}
}
// Helper function for log base 10
Math.log10 = Math.log10 || function(x) {
return Math.log(x) / Math.LN10;
};
// Toggle hip input visibility based on gender
document.getElementById('genderMale').onclick = function() {
document.getElementById('hipInputGroup').style.display = 'none';
};
document.getElementById('genderFemale').onclick = function() {
document.getElementById('hipInputGroup').style.display = 'block';
};
// Initial state for hip input
document.addEventListener('DOMContentLoaded', function() {
if (document.getElementById('genderMale').checked) {
document.getElementById('hipInputGroup').style.display = 'none';
}
});
Understanding Your Body Fat Percentage
Body fat percentage is a crucial health metric that represents the proportion of fat your body holds compared to your total body weight. Unlike Body Mass Index (BMI), which only considers height and weight, body fat percentage provides a more accurate picture of your body composition, distinguishing between fat mass and lean mass (muscle, bone, organs, water).
Why is Body Fat Percentage Important?
Maintaining a healthy body fat percentage is vital for overall health and well-being. Both excessively low and high body fat levels can pose health risks:
Too Low: Can lead to hormonal imbalances, weakened immune system, nutrient deficiencies, and impaired organ function. Essential fat is necessary for basic bodily functions.
Too High: Increases the risk of chronic diseases such as heart disease, type 2 diabetes, high blood pressure, certain cancers, and sleep apnea.
For athletes, body fat percentage is often monitored to optimize performance, as lower body fat can contribute to greater agility and endurance, while sufficient fat is needed for energy reserves.
Methods for Measuring Body Fat
There are several methods to estimate body fat percentage, 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. Highly accurate but requires specialized equipment.
Bioelectrical Impedance Analysis (BIA): Uses a small electrical current passed through the body. Fat-free mass conducts electricity better than fat mass. Accuracy can vary based on hydration levels.
Skinfold Calipers: Measures the thickness of skinfolds at various sites on the body. Requires a skilled technician for accurate results.
Circumference Measurements (like the US Navy Method): Uses body measurements (e.g., waist, neck, hip, height) in a formula to estimate body fat. This method is convenient and can be done at home, though it's less precise than laboratory methods.
About the US Navy Body Fat Calculator
The calculator above utilizes the US Navy Body Fat Formula, a widely recognized and practical method for estimating body fat percentage using simple body measurements. This method is popular due to its accessibility and ease of use, requiring only a tape measure.
For Women:Body Fat % = 163.205 * log10(waist + hip - neck) - 97.684 * log10(height) - 78.387
It's important to take measurements accurately and consistently for the best results. For example, waist circumference should be measured at the navel for men, and at the narrowest point for women. Neck circumference is typically measured just below the larynx.
Body Fat Percentage Ranges
Here are general guidelines for healthy body fat percentages, though individual needs may vary based on age, activity level, and genetics:
For Men:
Essential Fat: 2-5%
Athletes: 6-13%
Fitness: 14-17%
Average: 18-24%
Obese: 25% and above
For Women:
Essential Fat: 10-13%
Athletes: 14-20%
Fitness: 21-24%
Average: 25-31%
Obese: 32% and above
Remember, these are general guidelines. Consult with a healthcare professional or a certified fitness expert to interpret your results and determine what's healthy for your specific body and goals.