Calculate your body composition using the U.S. Navy Method.
Male
Female
Your Results:
0%
function toggleHipField() {
var gender = document.getElementById("bfGender").value;
var hipField = document.getElementById("hipField");
if (gender === "female") {
hipField.style.display = "block";
} else {
hipField.style.display = "none";
}
}
function calculateBodyFat() {
var gender = document.getElementById("bfGender").value;
var weight = parseFloat(document.getElementById("bfWeight").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 resultDiv = document.getElementById("bfResult");
var outputValue = document.getElementById("bfOutputValue");
var description = document.getElementById("bfDescription");
var massText = document.getElementById("bfMass");
if (!weight || !height || !neck || !waist || (gender === "female" && !hip)) {
alert("Please enter all required measurements.");
return;
}
var bodyFat = 0;
if (gender === "male") {
// US Navy Formula for Men: 495 / (1.0324 – 0.19077 * log10(waist – neck) + 0.15456 * log10(height)) – 450
bodyFat = 495 / (1.0324 – 0.19077 * (Math.log10(waist – neck)) + 0.15456 * (Math.log10(height))) – 450;
} else {
// US Navy Formula for Women: 495 / (1.29579 – 0.35004 * log10(waist + hip – neck) + 0.22100 * log10(height)) – 450
bodyFat = 495 / (1.29579 – 0.35004 * (Math.log10(waist + hip – neck)) + 0.22100 * (Math.log10(height))) – 450;
}
if (isNaN(bodyFat) || bodyFat <= 0) {
alert("Please check your measurements. The formula could not produce a valid result.");
return;
}
var finalBF = bodyFat.toFixed(1);
outputValue.innerHTML = finalBF + "%";
resultDiv.style.display = "block";
var category = "";
if (gender === "male") {
if (bodyFat < 6) category = "Essential Fat";
else if (bodyFat < 14) category = "Athlete";
else if (bodyFat < 18) category = "Fitness";
else if (bodyFat < 25) category = "Average";
else category = "Obese";
} else {
if (bodyFat < 14) category = "Essential Fat";
else if (bodyFat < 21) category = "Athlete";
else if (bodyFat < 25) category = "Fitness";
else if (bodyFat < 32) category = "Average";
else category = "Obese";
}
var fatMass = (weight * (bodyFat / 100)).toFixed(1);
var leanMass = (weight – fatMass).toFixed(1);
description.innerHTML = "Category: " + category;
massText.innerHTML = "Fat Mass: " + fatMass + " kg | Lean Mass: " + leanMass + " kg";
}
Understanding Your Body Fat Percentage
Body fat percentage is a much more accurate health marker than total body weight or Body Mass Index (BMI). While weight tells you how much you weigh, body fat percentage tells you what that weight consists of. This calculator uses the U.S. Navy Method, a widely recognized estimation formula that relies on circumference measurements to estimate body composition.
How the U.S. Navy Formula Works
The Navy Method was developed by the U.S. Naval Health Research Center. It provides a non-invasive way to track body composition changes over time. The formula takes into account your height and specific girth measurements:
For Men: It measures the neck and the waist (at the navel).
For Women: It measures the neck, waist (narrowest point), and hips (widest point).
Because muscle is denser than fat, people with higher muscle mass may weigh more but have a lower body fat percentage. Using circumference measurements helps account for the "shape" of the body, which is strongly correlated with fat distribution.
Healthy Body Fat Ranges
The ideal percentage varies significantly based on gender and age. Generally, the following categories are used for classification:
Category
Men
Women
Essential Fat
2-5%
10-13%
Athletes
6-13%
14-20%
Fitness
14-17%
21-24%
Average
18-24%
25-31%
Obese
25%+
32%+
Tips for Accurate Measurement
To get the most consistent results from this calculator, follow these measurement protocols:
Use a flexible tape measure: A cloth or soft plastic tailor's tape is best.
Measure on bare skin: Do not measure over clothing, as it adds unnecessary bulk.
The Neck: Measure just below the larynx (Adam's apple), pulling the tape snug but not tight.
The Waist: For men, measure at the level of the belly button. For women, measure at the narrowest part of the torso (natural waist).
The Hips (Women Only): Measure at the widest point of the buttocks/hips.
Consistency is key: Measure at the same time of day (preferably in the morning before eating) to avoid fluctuations due to bloating or hydration.
Practical Example
Suppose a 180 cm tall male weighs 85 kg. He has a neck circumference of 40 cm and a waist circumference of 92 cm. According to the formula, his body fat would be approximately 19.5%, placing him in the "Average" health category. If he maintains the same weight but reduces his waist to 88 cm through exercise, his body fat would drop to roughly 17%, moving him into the "Fitness" category.