function calculateBodyFat() {
var gender = document.querySelector('input[name="gender"]:checked').value;
var height = parseFloat(document.getElementById('bfHeight').value);
var neck = parseFloat(document.getElementById('bfNeck').value);
var waist = parseFloat(document.getElementById('bfWaist').value);
var hip = parseFloat(document.getElementById('bfHip').value) || 0;
var resultArea = document.getElementById('bf-result-area');
var bfValueDisplay = document.getElementById('bfValue');
var bfStatusDisplay = document.getElementById('bfStatus');
if (!height || !neck || !waist || (gender === 'female' && !hip)) {
alert("Please fill in all fields correctly.");
return;
}
var bodyFat = 0;
if (gender === 'male') {
// Navy Formula for Men (Imperial):
// 86.010 * log10(waist – neck) – 70.041 * log10(height) + 36.76
bodyFat = 86.010 * Math.log10(waist – neck) – 70.041 * Math.log10(height) + 36.76;
} else {
// Navy Formula for Women (Imperial):
// 163.205 * log10(waist + hip – neck) – 97.684 * log10(height) – 78.387
bodyFat = 163.205 * Math.log10(waist + hip – neck) – 97.684 * Math.log10(height) – 78.387;
}
if (isNaN(bodyFat) || bodyFat 60) {
alert("Please check your measurements. The results are outside normal physiological ranges.");
return;
}
var status = "";
var color = "#27ae60";
if (gender === 'male') {
if (bodyFat < 6) { status = "Essential Fat"; color = "#3498db"; }
else if (bodyFat < 14) { status = "Athletes"; color = "#2ecc71"; }
else if (bodyFat < 18) { status = "Fitness"; color = "#27ae60"; }
else if (bodyFat < 25) { status = "Average"; color = "#f1c40f"; }
else { status = "Obese"; color = "#e74c3c"; }
} else {
if (bodyFat < 14) { status = "Essential Fat"; color = "#3498db"; }
else if (bodyFat < 21) { status = "Athletes"; color = "#2ecc71"; }
else if (bodyFat < 25) { status = "Fitness"; color = "#27ae60"; }
else if (bodyFat < 32) { status = "Average"; color = "#f1c40f"; }
else { status = "Obese"; color = "#e74c3c"; }
}
bfValueDisplay.innerHTML = bodyFat.toFixed(1) + "%";
bfValueDisplay.style.color = color;
bfStatusDisplay.innerHTML = "Category: " + status;
bfStatusDisplay.style.color = color;
resultArea.style.display = 'block';
}
Understanding Your Body Fat Percentage
Body fat percentage is a much more accurate metric for health and fitness than Body Mass Index (BMI) or total body weight. While weight tells you how much you weigh, it doesn't distinguish between muscle, bone, and fat. This Body Fat Calculator uses the U.S. Navy Method, a scientifically validated formula used by the military to estimate body composition using simple tape measurements.
How to Take Accurate Measurements
To get the most accurate result from this calculator, follow these measurement guidelines:
Height: Measure without shoes, standing straight against a wall.
Neck: Measure below the larynx (Adam's apple), with the tape slanting slightly downward toward the front. Avoid "shrugging" your neck.
Waist (Men): Measure horizontally around the navel (belly button). Do not suck in your stomach.
Waist (Women): Measure at the narrowest part of the torso (natural waistline), usually above the belly button.
Hips (Women only): Measure at the widest point of the buttocks/hips.
Body Fat Categories for Men and Women
The American Council on Exercise (ACE) categorizes body fat percentages as follows:
Description
Women
Men
Essential fat
10–13%
2–5%
Athletes
14–20%
6–13%
Fitness
21–24%
14–17%
Average
25–31%
18–24%
Obese
32%+
25%+
Example Calculations
Example 1 (Male): A man who is 70 inches tall (5'10"), with a 16-inch neck and a 36-inch waist. The calculator would process these dimensions using the Navy formula to estimate a body fat of approximately 19.5%, placing him in the "Average" category.
Example 2 (Female): A woman who is 65 inches tall (5'5″), with a 13-inch neck, 28-inch waist, and 38-inch hips. The calculator estimates her body fat at approximately 23.8%, which falls within the "Fitness" category.
Why the Navy Method?
While DXA scans and hydrostatic weighing are the "gold standards" for body fat testing, they are expensive and inaccessible for most people. The Navy Method provides a reliable estimation with a margin of error of only 3-4% compared to clinical methods, making it the perfect tool for tracking progress in a weight loss or muscle-building journey from the comfort of your home.