function calculateBodyFat() {
var gender = document.getElementById("bf_gender").value;
var height = parseFloat(document.getElementById("bf_height").value);
var neck = parseFloat(document.getElementById("bf_neck").value);
var waist = parseFloat(document.getElementById("bf_waist").value);
var hip = parseFloat(document.getElementById("bf_hip").value) || 0;
var resultDiv = document.getElementById("bf_result");
var valueDiv = document.getElementById("bf_value");
var categoryDiv = document.getElementById("bf_category");
if (!height || !neck || !waist || (gender === "female" && !hip)) {
alert("Please fill in all fields with valid numbers.");
return;
}
var bodyFat = 0;
if (gender === "male") {
// US Navy Formula for Men (Imperial)
bodyFat = 86.010 * Math.log10(waist – neck) – 70.041 * Math.log10(height) + 36.76;
} else {
// US Navy Formula for Women (Imperial)
bodyFat = 163.205 * Math.log10(waist + hip – neck) – 97.684 * Math.log10(height) – 78.387;
}
if (isNaN(bodyFat) || bodyFat < 0) {
valueDiv.innerHTML = "Error";
categoryDiv.innerHTML = "Check your measurements. Calculations resulted in an impossible value.";
} else {
var bfFixed = bodyFat.toFixed(1);
valueDiv.innerHTML = bfFixed + "%";
var category = "";
var color = "";
if (gender === "male") {
if (bodyFat < 6) { category = "Essential Fat"; color = "#3498db"; }
else if (bodyFat < 14) { category = "Athletes"; color = "#2ecc71"; }
else if (bodyFat < 18) { category = "Fitness"; color = "#27ae60"; }
else if (bodyFat < 25) { category = "Average"; color = "#f1c40f"; }
else { category = "Obese"; color = "#e74c3c"; }
} else {
if (bodyFat < 14) { category = "Essential Fat"; color = "#3498db"; }
else if (bodyFat < 21) { category = "Athletes"; color = "#2ecc71"; }
else if (bodyFat < 25) { category = "Fitness"; color = "#27ae60"; }
else if (bodyFat < 32) { category = "Average"; color = "#f1c40f"; }
else { category = "Obese"; color = "#e74c3c"; }
}
categoryDiv.innerHTML = "Category: " + category;
resultDiv.style.backgroundColor = color + "15";
valueDiv.style.color = color;
}
resultDiv.style.display = "block";
}
Understanding the U.S. Navy Body Fat Calculator
Body fat percentage is a much more accurate health marker than total body weight or Body Mass Index (BMI). While BMI only considers height and weight, the Navy Method Body Fat Calculator uses circumference measurements to estimate lean body mass versus adipose tissue.
How the Navy Method Works
Developed by the U.S. Navy, this formula was designed to provide a quick and reliable way to estimate body fat percentage without expensive equipment like DEXA scans or hydrostatic weighing. It uses the relationship between your height and the circumference of your neck, waist, and (for women) hips.
How to Get Accurate Measurements
To ensure your results are as accurate as possible, follow these measuring tips:
Height: Measure while standing straight, without shoes.
Neck: Measure just below the larynx (Adam's apple), with the tape sloping slightly downward to the front.
Waist:
Men: Measure at the navel (belly button).
Women: Measure at the narrowest point of the natural waistline (usually above the navel).
Hips (Women only): Measure at the widest point of the buttocks.
Body Fat Percentage Categories
According to the American Council on Exercise (ACE), here are the standard body fat ranges for men and women:
Category
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%+
Navy Method vs. BMI
BMI is often criticized because it does not distinguish between muscle and fat. For example, a bodybuilder might have a BMI that classifies them as "obese" despite having very low body fat. The Navy Method is superior for active individuals because it accounts for the physical dimensions of the torso, where fat accumulation is most significant for health risks.