Body Fat Index Calculator

Estimate your body fat percentage using the U.S. Navy method.

Gender:
Male Female

Height (inches):

Neck Circumference (inches):

Waist Circumference (inches):

Hip Circumference (inches):

/* Basic styling for the calculator */ .calculator-container { background-color: #f9f9f9; border: 1px solid #ddd; padding: 20px; border-radius: 8px; max-width: 500px; margin: 20px auto; font-family: Arial, sans-serif; } .calculator-container h2 { text-align: center; color: #333; margin-bottom: 20px; } .form-group { margin-bottom: 15px; } .form-group label { display: block; margin-bottom: 5px; font-weight: bold; color: #555; } .form-group input[type="number"], .form-group input[type="text"] { width: calc(100% – 22px); padding: 10px; border: 1px solid #ccc; border-radius: 4px; box-sizing: border-box; } .form-group input[type="radio"] { margin-right: 5px; } button { background-color: #007bff; color: white; padding: 12px 20px; border: none; border-radius: 4px; cursor: pointer; font-size: 16px; width: 100%; transition: background-color 0.3s ease; } button:hover { background-color: #0056b3; } .calculator-result { margin-top: 20px; padding: 15px; border: 1px solid #e0e0e0; border-radius: 4px; background-color: #e9f7ef; color: #333; } .calculator-result h3 { margin-top: 0; color: #28a745; } .calculator-result p { margin-bottom: 5px; } // Polyfill for Math.log10 if not supported (though modern browsers do) if (!Math.log10) { Math.log10 = function(x) { return Math.log(x) / Math.LN10; }; } function calculateBodyFat() { var gender = document.querySelector('input[name="gender"]:checked').value; var height = parseFloat(document.getElementById('heightInches').value); var neck = parseFloat(document.getElementById('neckCircumferenceInches').value); var waist = parseFloat(document.getElementById('waistCircumferenceInches').value); var hip = parseFloat(document.getElementById('hipCircumferenceInches').value); var resultDiv = document.getElementById('result'); resultDiv.innerHTML = "; // Clear previous results // Input validation if (isNaN(height) || height <= 0) { resultDiv.innerHTML = 'Please enter a valid height (e.g., 70 for 5\'10").'; return; } if (isNaN(neck) || neck <= 0) { resultDiv.innerHTML = 'Please enter a valid neck circumference.'; return; } if (isNaN(waist) || waist <= 0) { resultDiv.innerHTML = 'Please enter a valid waist circumference.'; return; } var bodyFatPercentage; var bodyFatCategory = ''; if (gender === 'male') { // Formula for men (US Navy method, inches) // BF% = 86.010 * log10(waist – neck) – 70.041 * log10(height) + 36.76 if (waist <= neck) { resultDiv.innerHTML = 'For men, waist circumference must be greater than neck circumference for a valid calculation.'; return; } bodyFatPercentage = 86.010 * Math.log10(waist – neck) – 70.041 * Math.log10(height) + 36.76; // Male Body Fat Categories (approximate ranges based on ACE guidelines) if (bodyFatPercentage = 6 && bodyFatPercentage = 14 && bodyFatPercentage = 18 && bodyFatPercentage <= 24) { bodyFatCategory = 'Acceptable'; } else { bodyFatCategory = 'Obese'; } } else { // female if (isNaN(hip) || hip <= 0) { resultDiv.innerHTML = 'Please enter a valid hip circumference for females.'; return; } // Formula for women (US Navy method, inches) // BF% = 163.205 * log10(waist + hip – neck) – 97.684 * log10(height) – 78.387 if ((waist + hip) <= neck) { resultDiv.innerHTML = 'For women, the sum of waist and hip circumference must be greater than neck circumference for a valid calculation.'; return; } bodyFatPercentage = 163.205 * Math.log10(waist + hip – neck) – 97.684 * Math.log10(height) – 78.387; // Female Body Fat Categories (approximate ranges based on ACE guidelines) if (bodyFatPercentage = 14 && bodyFatPercentage = 21 && bodyFatPercentage = 25 && bodyFatPercentage <= 31) { bodyFatCategory = 'Acceptable'; } else { bodyFatCategory = 'Obese'; } } // Ensure body fat percentage is within a reasonable range if (bodyFatPercentage 100) bodyFatPercentage = 100; resultDiv.innerHTML = '

Your Estimated Body Fat:

' + 'Body Fat Percentage: ' + bodyFatPercentage.toFixed(2) + '%' + 'Category: ' + bodyFatCategory + " + 'Note: This is an estimation based on the U.S. Navy method and should be used as a guide.'; } function toggleHipInput() { var genderMale = document.getElementById('genderMale'); var hipGroup = document.getElementById('hipCircumferenceGroup'); if (genderMale.checked) { // If male is selected hipGroup.style.display = 'none'; document.getElementById('hipCircumferenceInches').value = "; // Clear value when hidden } else { // If female is selected hipGroup.style.display = 'block'; } } // Initialize hip input visibility on page load document.addEventListener('DOMContentLoaded', function() { toggleHipInput(); });

Understanding Your Body Fat Percentage

Body fat percentage is a crucial metric that indicates the proportion of fat your body holds relative 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).

Why is Body Fat Percentage Important?

Maintaining a healthy body fat percentage is vital for overall health and well-being. Both excessively high and extremely low body fat levels can pose health risks:

High Body Fat: Can increase the risk of chronic diseases such as heart disease, type 2 diabetes, high blood pressure, certain cancers, and sleep apnea.
Low Body Fat: Essential fat is necessary for basic bodily functions. Too little body fat can lead to hormonal imbalances, impaired immune function, nutrient deficiencies, and reproductive issues, especially in women.

Knowing your body fat percentage can help you set realistic fitness goals, track progress more effectively than just weight, and understand your health risks better.

About the U.S. Navy Body Fat Calculator Method

While highly accurate methods like DEXA scans or hydrostatic weighing require specialized equipment, the U.S. Navy Body Fat Calculator offers a practical and widely used estimation method. It relies on a simple set of circumference measurements and your height to calculate an approximate body fat percentage. This method is popular due to its accessibility and reasonable accuracy for a non-laboratory setting.

How to Use This Calculator for Accurate Results

To get the most reliable estimate from this calculator, precise measurements are key. Use a flexible measuring tape and ensure it's snug but not compressing the skin. Take measurements multiple times and average them for consistency.

Height (inches): Measure your height without shoes.
Neck Circumference (inches): Measure horizontally just below the larynx (Adam's apple). Keep your head straight.
Waist Circumference (inches):
- For Men: Measure horizontally at the level of your navel (belly button).
- For Women: Measure horizontally at the narrowest part of your waist, usually above the navel.
Hip Circumference (inches) (for Women only): Measure horizontally at the largest protrusion of your buttocks.

Interpreting Your Body Fat Percentage

Once you've calculated your body fat percentage, you can compare it to general guidelines. These categories can vary slightly by source, but here are commonly accepted ranges:

Body Fat Categories for Men:

Essential Fat: 2-5%
Athletes: 6-13%
Fitness: 14-17%
Acceptable: 18-24%
Obese: 25% and above

Body Fat Categories for Women:

Essential Fat: 10-13%
Athletes: 14-20%
Fitness: 21-24%
Acceptable: 25-31%
Obese: 32% and above

Example Calculations:

Let's look at a couple of examples using the U.S. Navy method:

Male Example: A man with a height of 70 inches (5'10"), neck circumference of 15.5 inches, and waist circumference of 32 inches would have an estimated body fat percentage of approximately 12.23%, placing him in the 'Athletes' category.
Female Example: A woman with a height of 65 inches (5'5″), neck circumference of 12.5 inches, waist circumference of 28 inches, and hip circumference of 38 inches would have an estimated body fat percentage of approximately 26.57%, placing her in the 'Acceptable' category.

Important Considerations

Remember that this calculator provides an estimate. Factors such as individual body shape, muscle mass, hydration levels, and measurement technique can influence the results. For personalized health and fitness advice, always consult with a healthcare professional or a certified fitness expert.