Note: This calculation uses the U.S. Navy Circumference Method, which provides an estimate within 3-4% accuracy for most individuals.
Understanding Body Fat Percentage
Body fat percentage is the total mass of fat divided by total body mass, multiplied by 100. Unlike Body Mass Index (BMI), which only accounts for height and weight, body fat percentage distinguishes between lean muscle mass and adipose tissue (fat). This makes it a much more accurate indicator of fitness and health risks.
How to Take Accurate Measurements
To get the most accurate result from this calculator, follow these measurement protocols:
Height: Measure without shoes, standing straight against a wall.
Neck: Measure just below the larynx (Adam's apple), sloping slightly downward toward the front.
Waist: Men: Measure horizontally at the level of the navel.
Women: Measure horizontally at the narrowest point of the abdomen (usually just above the navel).
Hips (Women only): Measure horizontally at the widest point of the buttocks/hips.
Body Fat Categories (ACE Standards)
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% +
Realistic Example Calculation
Suppose a male individual stands 180 cm tall (approx. 5'11"), has a neck circumference of 40 cm, and a waist of 90 cm.
Using the U.S. Navy formula:
495 / (1.0324 - 0.19077 * log10(90 - 40) + 0.15456 * log10(180)) - 450 The resulting body fat would be approximately 17.6%, placing him in the "Fitness" category.
function toggleHipField() {
var gender = document.getElementById("gender").value;
var hipContainer = document.getElementById("hipContainer");
if (gender === "female") {
hipContainer.style.display = "block";
} else {
hipContainer.style.display = "none";
}
}
function updateLabels() {
var system = document.getElementById("units").value;
var suffix = (system === "metric") ? "(cm)" : "(in)";
document.getElementById("heightLabel").innerText = "Height " + suffix + ":";
document.getElementById("neckLabel").innerText = "Neck Circumference " + suffix + ":";
document.getElementById("waistLabel").innerText = "Waist Circumference " + suffix + ":";
document.getElementById("hipLabel").innerText = "Hip Circumference " + suffix + ":";
}
function calculateBodyFat() {
var gender = document.getElementById("gender").value;
var units = document.getElementById("units").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;
if (!height || !neck || !waist || (gender === "female" && !hip)) {
alert("Please fill in all required fields with valid numbers.");
return;
}
// Convert to metric if imperial for internal math
var h = height;
var n = neck;
var w = waist;
var hp = hip;
if (units === "imperial") {
h = height * 2.54;
n = neck * 2.54;
w = waist * 2.54;
hp = hip * 2.54;
}
var bf = 0;
if (gender === "male") {
// US Navy Formula for Men
// BF = 495 / (1.0324 – 0.19077 * log10(waist – neck) + 0.15456 * log10(height)) – 450
var logWaistNeck = Math.log10(w – n);
var logHeight = Math.log10(h);
bf = 495 / (1.0324 – 0.19077 * logWaistNeck + 0.15456 * logHeight) – 450;
} else {
// US Navy Formula for Women
// BF = 495 / (1.29579 – 0.35004 * log10(waist + hip – neck) + 0.22100 * log10(height)) – 450
var logWaistHipNeck = Math.log10(w + hp – n);
var logHeightFem = Math.log10(h);
bf = 495 / (1.29579 – 0.35004 * logWaistHipNeck + 0.22100 * logHeightFem) – 450;
}
if (bf < 0) bf = 2; // Limit lower bound for physiological reasons
var displayVal = bf.toFixed(1);
document.getElementById("fatPercentDisplay").innerText = displayVal;
var category = "";
if (gender === "male") {
if (bf < 6) category = "Category: Essential Fat";
else if (bf < 14) category = "Category: Athlete";
else if (bf < 18) category = "Category: Fitness";
else if (bf < 25) category = "Category: Average";
else category = "Category: Obese";
} else {
if (bf < 14) category = "Category: Essential Fat";
else if (bf < 21) category = "Category: Athlete";
else if (bf < 25) category = "Category: Fitness";
else if (bf < 32) category = "Category: Average";
else category = "Category: Obese";
}
document.getElementById("categoryDisplay").innerText = category;
document.getElementById("results").style.display = "block";
document.getElementById("results").scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}