function toggleHipInput() {
var gender = document.getElementById("gender").value;
var hipInputGroup = document.getElementById("hipInputGroup");
if (gender === "female") {
hipInputGroup.style.display = "block";
} else {
hipInputGroup.style.display = "none";
}
}
function calculateBodyFat() {
var gender = document.getElementById("gender").value;
var age = parseFloat(document.getElementById("age").value);
var weight = parseFloat(document.getElementById("weight").value); // Not used in Navy formula, but good to have for other calculations
var height = parseFloat(document.getElementById("height").value);
var neck = parseFloat(document.getElementById("neckCircumference").value);
var waist = parseFloat(document.getElementById("waistCircumference").value);
var hip = parseFloat(document.getElementById("hipCircumference").value);
var resultDiv = document.getElementById("result");
resultDiv.style.color = "#333"; // Reset color
if (isNaN(age) || isNaN(weight) || isNaN(height) || isNaN(neck) || isNaN(waist) ||
age <= 0 || weight <= 0 || height <= 0 || neck <= 0 || waist <= 0) {
resultDiv.innerHTML = "
";
return;
}
if (gender === "female" && isNaN(hip) || (gender === "female" && hip <= 0)) {
resultDiv.innerHTML = "
";
return;
}
var bodyFatPercentage;
var classification = "";
if (gender === "male") {
var logWaistNeck = Math.log10(waist – neck);
var logHeight = Math.log10(height);
if (isNaN(logWaistNeck) || (waist – neck) <= 0) {
resultDiv.innerHTML = "
";
return;
}
bodyFatPercentage = 86.010 * logWaistNeck – 70.041 * logHeight + 36.76;
// Male Body Fat Categories (ACSM Guidelines)
if (age >= 20 && age <= 29) {
if (bodyFatPercentage = 6 && bodyFatPercentage = 14 && bodyFatPercentage = 18 && bodyFatPercentage = 30 && age <= 39) {
if (bodyFatPercentage = 7 && bodyFatPercentage = 15 && bodyFatPercentage = 21 && bodyFatPercentage = 40 && age <= 49) {
if (bodyFatPercentage = 8 && bodyFatPercentage = 17 && bodyFatPercentage = 22 && bodyFatPercentage = 50 && age <= 59) {
if (bodyFatPercentage = 9 && bodyFatPercentage = 18 && bodyFatPercentage = 23 && bodyFatPercentage = 60) {
if (bodyFatPercentage = 10 && bodyFatPercentage = 20 && bodyFatPercentage = 25 && bodyFatPercentage <= 31) classification = "Acceptable";
else classification = "Obese";
} else { // Age < 20, use general guidelines
if (bodyFatPercentage = 5 && bodyFatPercentage = 11 && bodyFatPercentage = 15 && bodyFatPercentage <= 20) classification = "Acceptable";
else classification = "Obese";
}
} else { // Female
var logWaistHipNeck = Math.log10(waist + hip – neck);
var logHeight = Math.log10(height);
if (isNaN(logWaistHipNeck) || (waist + hip – neck) <= 0) {
resultDiv.innerHTML = "
";
return;
}
bodyFatPercentage = 163.205 * logWaistHipNeck – 97.684 * logHeight – 78.387;
// Female Body Fat Categories (ACSM Guidelines)
if (age >= 20 && age <= 29) {
if (bodyFatPercentage = 14 && bodyFatPercentage = 21 && bodyFatPercentage = 25 && bodyFatPercentage = 30 && age <= 39) {
if (bodyFatPercentage = 15 && bodyFatPercentage = 22 && bodyFatPercentage = 26 && bodyFatPercentage = 40 && age <= 49) {
if (bodyFatPercentage = 16 && bodyFatPercentage = 23 && bodyFatPercentage = 28 && bodyFatPercentage = 50 && age <= 59) {
if (bodyFatPercentage = 17 && bodyFatPercentage = 24 && bodyFatPercentage = 29 && bodyFatPercentage = 60) {
if (bodyFatPercentage = 18 && bodyFatPercentage = 25 && bodyFatPercentage = 30 && bodyFatPercentage <= 37) classification = "Acceptable";
else classification = "Obese";
} else { // Age < 20, use general guidelines
if (bodyFatPercentage = 10 && bodyFatPercentage = 16 && bodyFatPercentage = 20 && bodyFatPercentage <= 25) classification = "Acceptable";
else classification = "Obese";
}
}
if (bodyFatPercentage 100) bodyFatPercentage = 100; // Cap at 100%
resultDiv.innerHTML = "Your estimated Body Fat Percentage is:
";
}
// Initial call to set hip input visibility based on default gender
toggleHipInput();
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 directly measures the amount of adipose tissue (fat) in your body. This makes it a more accurate indicator of health risks associated with body composition.
Why is Body Fat Percentage Important?
Maintaining a healthy body fat percentage is vital for overall well-being. Both excessively low and excessively high body fat levels can pose health risks:
- Too Low: Can lead to hormonal imbalances, weakened immune function, 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.
How is Body Fat Measured?
There are several methods to measure body fat, each with varying degrees of accuracy and cost:
- Skinfold Calipers: Measures the thickness of subcutaneous fat at various sites.
- Bioelectrical Impedance Analysis (BIA): Sends a small electrical current through the body to estimate body composition.
- Hydrostatic Weighing (Underwater Weighing): Considered a gold standard, it measures body density.
- DEXA Scan (Dual-energy X-ray Absorptiometry): Highly accurate, it uses X-rays to differentiate between bone, lean mass, and fat.
- Circumference Measurements (like this calculator): Uses specific body measurements and formulas to estimate body fat. While less precise than DEXA or hydrostatic weighing, it's a convenient and accessible method.
About This Calculator (U.S. Navy Method)
This calculator utilizes the U.S. Navy Body Fat Formula, a widely recognized and practical method for estimating body fat percentage using simple circumference measurements. It requires your gender, age, height, neck, waist, and for females, hip circumference. The formulas are:
- For Men:
Body Fat % = 86.010 * log10(waist - neck) - 70.041 * log10(height) + 36.76
- For Women:
Body Fat % = 163.205 * log10(waist + hip - neck) - 97.684 * log10(height) - 78.387
All measurements should be taken in inches. For best accuracy, measure your waist at the navel (or largest circumference), neck just below the larynx, and hips at the largest circumference.
Interpreting Your Results
The calculated body fat percentage will fall into one of several categories, which vary slightly by age and gender. Here are general guidelines (based on ACSM):
| Category |
Women (General) |
Men (General) |
| Essential Fat |
10-13% |
2-5% |
| Athletes |
14-20% |
6-13% |
| Fitness |
21-24% |
14-17% |
| Acceptable |
25-31% |
18-24% |
| Obese |
32%+ |
25%+ |
Note: These are general guidelines. Individual needs may vary. Consult a healthcare professional for personalized advice.
Maintaining Healthy Body Fat Levels
Achieving and maintaining a healthy body fat percentage involves a combination of balanced nutrition, regular physical activity, and a healthy lifestyle. Focus on:
- Balanced Diet: Emphasize whole foods, lean proteins, fruits, vegetables, and healthy fats.
- Regular Exercise: Incorporate both cardiovascular workouts and strength training to build muscle and burn fat.
- Adequate Sleep: Poor sleep can disrupt hormones that regulate appetite and fat storage.
- Stress Management: Chronic stress can lead to increased fat storage, particularly around the abdomen.
Remember, this calculator provides an estimate. For a precise assessment and personalized health plan, it's always best to consult with a doctor or a certified fitness professional.