function toggleHipInput() {
var gender = document.getElementById("gender").value;
var hipContainer = document.getElementById("hip-container");
if (gender === "female") {
hipContainer.style.display = "block";
} else {
hipContainer.style.display = "none";
}
}
function calculateBodyFat() {
var gender = document.getElementById("gender").value;
var height = parseFloat(document.getElementById("height").value);
var neck = parseFloat(document.getElementById("neck").value);
var waist = parseFloat(document.getElementById("waist").value);
var hip = parseFloat(document.getElementById("hip").value) || 0;
var resultBox = document.getElementById("result-box");
var bfDisplay = document.getElementById("bf-percentage");
var catDisplay = document.getElementById("bf-category");
if (!height || !neck || !waist || (gender === "female" && !hip)) {
alert("Please fill in all required measurements.");
return;
}
var bodyFat = 0;
if (gender === "male") {
// US Navy Formula for Men (Inches)
bodyFat = 86.010 * Math.log10(waist – neck) – 70.041 * Math.log10(height) + 36.76;
} else {
// US Navy Formula for Women (Inches)
bodyFat = 163.205 * Math.log10(waist + hip – neck) – 97.684 * Math.log10(height) – 78.387;
}
bodyFat = Math.round(bodyFat * 10) / 10;
resultBox.style.display = "block";
bfDisplay.innerHTML = "Estimated Body Fat: " + bodyFat + "%";
var category = "";
var color = "";
if (gender === "male") {
if (bodyFat < 6) { category = "Essential Fat"; color = "#3498db"; }
else if (bodyFat < 14) { category = "Athlete"; 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 = "Athlete"; color = "#2ecc71"; }
else if (bodyFat < 25) { category = "Fitness"; color = "#27ae60"; }
else if (bodyFat < 32) { category = "Average"; color = "#f1c40f"; }
else { category = "Obese"; color = "#e74c3c"; }
}
catDisplay.innerHTML = "Category: " + category;
resultBox.style.backgroundColor = color + "22";
bfDisplay.style.color = color;
catDisplay.style.color = color;
}
How the US Navy Body Fat Calculator Works
The US Navy body fat formula is a widely used method for estimating body composition without the need for expensive equipment like DXA scans or hydrostatic weighing. By measuring the circumference of specific body parts, the algorithm can estimate your body fat percentage with a reasonable degree of accuracy.
The Importance of Measuring Body Fat
Unlike Body Mass Index (BMI), which only looks at your weight relative to your height, body fat percentage tells you how much of your weight is actually adipose tissue. This is a far more accurate indicator of physical fitness and health risks. High body fat percentages are often linked to cardiovascular disease, type 2 diabetes, and metabolic syndrome.
Body Fat Categories Breakdown
Understanding where you fall in the body fat spectrum helps in setting realistic fitness goals. Here are the general ranges provided by the American Council on Exercise (ACE):
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%+
How to Take Accurate Measurements
For the most accurate results from this calculator, follow these measurement tips:
Waist: Measure at the narrowest point for women and at the navel (belly button) for men.
Neck: Measure just below the larynx (Adam's apple), sloping slightly downward toward the front.
Height: Measure without shoes, standing straight against a flat wall.
Hips (Women only): Measure at the widest point of the buttocks.
Calculation Example
Consider a male who is 70 inches tall, with a 34-inch waist and a 15-inch neck.
Using the formula: 86.010 * log10(34 - 15) - 70.041 * log10(70) + 36.76.
The result would be approximately 17.6% Body Fat, placing him in the "Fitness" category.