U.S. Navy Method (Scientific Body Composition Analysis)
Your Results:
0%
Category: Normal
How the Body Fat Calculator Works
This calculator uses the U.S. Navy Fitness Formula, a widely recognized method for estimating body composition without expensive DEXA scans or hydrostatic weighing. While no mathematical formula is 100% accurate for everyone, the Navy Method is known for its reliability in clinical and fitness settings when skinfold calipers are unavailable.
The Measurement Guide
To ensure the most accurate result, follow these measurement protocols:
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 part of the abdomen (usually above the navel).
Hips (Women only): Measure the widest horizontal circumference around the buttocks.
Height: Stand straight against a wall without shoes.
Understanding Your Results
Body fat percentage is a better indicator of health than BMI because it distinguishes between lean muscle mass and adipose tissue (fat). Here is a breakdown of the standard health categories 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%+
Example Calculation
If a male is 180cm tall, has a 40cm neck, and a 90cm waist:
The formula calculates the log difference between waist and neck.
It factors in the log of the height.
Final estimated body fat: ~18.4% (Category: Average).
Disclaimer: This calculator provides an estimate for informational purposes only. Consult with a healthcare professional or certified fitness trainer for a comprehensive physical assessment.
function calculateBF() {
var genderElements = document.getElementsByName('gender');
var gender = 'male';
for (var i = 0; i < genderElements.length; i++) {
if (genderElements[i].checked) {
gender = genderElements[i].value;
break;
}
}
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;
}
var bodyFat = 0;
if (gender === 'male') {
// Navy Formula for Men: 495 / (1.0324 – 0.19077 * log10(waist – neck) + 0.15456 * log10(height)) – 450
var logVal = Math.log10(waist – neck);
var logHeight = Math.log10(height);
bodyFat = 495 / (1.0324 – 0.19077 * logVal + 0.15456 * logHeight) – 450;
} else {
// Navy Formula for Women: 495 / (1.29579 – 0.35004 * log10(waist + hip – neck) + 0.22100 * log10(height)) – 450
var logVal = Math.log10(waist + hip – neck);
var logHeight = Math.log10(height);
bodyFat = 495 / (1.29579 – 0.35004 * logVal + 0.22100 * logHeight) – 450;
}
if (bodyFat < 2) bodyFat = 2; // Threshold for survival fat
var category = "";
var advice = "";
if (gender === 'male') {
if (bodyFat < 6) { category = "Essential Fat"; advice = "Very low body fat level, typical of competitive athletes."; }
else if (bodyFat < 14) { category = "Athletes"; advice = "Excellent physical condition and high muscle definition."; }
else if (bodyFat < 18) { category = "Fitness"; advice = "Good health and muscle definition."; }
else if (bodyFat < 25) { category = "Average"; advice = "Typical range for healthy men."; }
else { category = "Obese"; advice = "Consider lifestyle adjustments to lower health risks."; }
} else {
if (bodyFat < 14) { category = "Essential Fat"; advice = "Very low body fat level, typical of competitive athletes."; }
else if (bodyFat < 21) { category = "Athletes"; advice = "Excellent physical condition and high muscle definition."; }
else if (bodyFat < 25) { category = "Fitness"; advice = "Good health and lean appearance."; }
else if (bodyFat < 32) { category = "Average"; advice = "Typical range for healthy women."; }
else { category = "Obese"; advice = "Consider lifestyle adjustments to lower health risks."; }
}
document.getElementById('bf-percentage').innerText = bodyFat.toFixed(1) + "%";
document.getElementById('bf-category').innerText = "Category: " + category;
document.getElementById('bf-advice').innerText = advice;
document.getElementById('bf-result-area').style.display = 'block';
document.getElementById('bf-result-area').scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}