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);
var resultDiv = document.getElementById("bf_result_box");
var valueSpan = document.getElementById("bf_value");
var categorySpan = document.getElementById("bf_category");
if (!height || !neck || !waist || (gender === "female" && !hip)) {
alert("Please fill in all required measurements.");
return;
}
var bf = 0;
if (gender === "male") {
// US Navy Formula for Men (Metric)
bf = 495 / (1.0324 – 0.19077 * Math.log10(waist – neck) + 0.15456 * Math.log10(height)) – 450;
} else {
// US Navy Formula for Women (Metric)
bf = 495 / (1.29579 – 0.35004 * Math.log10(waist + hip – neck) + 0.22100 * Math.log10(height)) – 450;
}
bf = bf.toFixed(1);
valueSpan.innerHTML = bf + "% Body Fat";
resultDiv.style.display = "block";
var category = "";
var color = "";
if (gender === "male") {
if (bf < 6) { category = "Essential Fat"; color = "#3498db"; }
else if (bf < 14) { category = "Athletes"; color = "#2ecc71"; }
else if (bf < 18) { category = "Fitness"; color = "#27ae60"; }
else if (bf < 25) { category = "Average"; color = "#f1c40f"; }
else { category = "Obese"; color = "#e74c3c"; }
} else {
if (bf < 14) { category = "Essential Fat"; color = "#3498db"; }
else if (bf < 21) { category = "Athletes"; color = "#2ecc71"; }
else if (bf < 25) { category = "Fitness"; color = "#27ae60"; }
else if (bf < 32) { category = "Average"; color = "#f1c40f"; }
else { category = "Obese"; color = "#e74c3c"; }
}
categorySpan.innerHTML = "Category: " + category;
categorySpan.style.color = color;
resultDiv.style.backgroundColor = color + "15";
resultDiv.style.border = "2px solid " + color;
}
Understanding Your Body Fat Percentage
While total body weight is a common metric for health, it doesn't tell the whole story. Body fat percentage is a much more accurate indicator of fitness and health risks because it distinguishes between lean muscle mass and adipose tissue (fat). This calculator uses the U.S. Navy Fitness Formula, a widely recognized method that estimates body fat based on specific circumference measurements.
Why Use the Navy Method?
The U.S. Navy Method is popular because it requires no expensive equipment like DEXA scans or hydrostatic weighing. All you need is a simple measuring tape. Research has shown that for most people, these measurements correlate closely with more advanced clinical tests. It focuses on the areas where the body tends to store fat most: the abdominal region for men and the hips and waist for women.
Calculation Examples
Example 1: Active Male
Height: 180cm, Neck: 41cm, Waist: 85cm. Result: ~14.8% (Fitness Category)
Example 2: Average Female
Height: 165cm, Neck: 35cm, Waist: 78cm, Hips: 98cm. Result: ~26.4% (Average Category)
Healthy Body Fat Ranges
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 Measure Correctly
To get the most accurate results, follow these measurement tips:
Height: Measure without shoes, standing straight against a wall.
Waist: For men, measure at the navel. For women, measure at the narrowest point (natural waist).
Neck: Measure below the larynx (Adam's apple), sloping slightly downward toward the front.
Hips (Women only): Measure at the widest point of the buttocks.
Disclaimer: This calculator is for educational purposes and is not a substitute for professional medical advice. Always consult with a healthcare provider before beginning a new fitness or diet regimen.