function toggleHips() {
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 hips = parseFloat(document.getElementById("hips").value) || 0;
var resultArea = document.getElementById("bf-result-area");
var percentageDisplay = document.getElementById("bf-percentage");
var categoryDisplay = document.getElementById("bf-category");
if (isNaN(height) || isNaN(neck) || isNaN(waist) || (gender === "female" && isNaN(hips))) {
alert("Please enter all required measurements.");
return;
}
var bodyFat = 0;
if (gender === "male") {
// 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 {
// Navy Formula for Women: 495 / (1.29579 – 0.35004 * log10(waist + hips – neck) + 0.22100 * log10(height)) – 450
bodyFat = 495 / (1.29579 – 0.35004 * (Math.log10(waist + hips – neck)) + 0.22100 * (Math.log10(height))) – 450;
}
var finalBf = bodyFat.toFixed(1);
resultArea.style.display = "block";
percentageDisplay.innerHTML = finalBf + "%";
var category = "";
var bgColor = "";
if (gender === "male") {
if (finalBf < 6) { category = "Essential Fat"; bgColor = "#e8f6f3"; }
else if (finalBf < 14) { category = "Athletes"; bgColor = "#d4efdf"; }
else if (finalBf < 18) { category = "Fitness"; bgColor = "#d4efdf"; }
else if (finalBf < 25) { category = "Average"; bgColor = "#fcf3cf"; }
else { category = "Obese"; bgColor = "#fadbd8"; }
} else {
if (finalBf < 14) { category = "Essential Fat"; bgColor = "#e8f6f3"; }
else if (finalBf < 21) { category = "Athletes"; bgColor = "#d4efdf"; }
else if (finalBf < 25) { category = "Fitness"; bgColor = "#d4efdf"; }
else if (finalBf < 32) { category = "Average"; bgColor = "#fcf3cf"; }
else { category = "Obese"; bgColor = "#fadbd8"; }
}
categoryDisplay.innerHTML = "Category: " + category;
resultArea.style.backgroundColor = bgColor;
}
Understanding Your Body Fat Percentage
Body fat percentage is a much more accurate health marker than Body Mass Index (BMI) or simple weight, as it distinguishes between muscle mass and fat mass. While weight can fluctuate based on hydration and glycogen levels, your body fat percentage tells you exactly what portion of your body is composed of adipose tissue.
What is the U.S. Navy Method?
The U.S. Navy Method is a widely recognized formula used to estimate body fat percentage without the need for expensive equipment like DEXA scans or hydrostatic weighing. It relies on circumference measurements of the neck, waist, and hips (for women) alongside height. While it has a margin of error of roughly 3-4%, it is highly effective for tracking progress over time because it is consistent and easy to perform at home.
Healthy Body Fat Ranges
Ideal body fat levels vary significantly based on gender and age. Women naturally require more body fat for hormonal health and reproductive function.
Essential Fat: Men (2-5%), Women (10-13%) – Necessary for basic physiological function.
Athletes: Men (6-13%), Women (14-20%) – High performance and low subcutaneous fat.
Fitness: Men (14-17%), Women (21-24%) – Healthy, lean appearance.
Average: Men (18-24%), Women (25-31%) – Standard healthy range for most adults.
Obese: Men (25%+), Women (32%+) – Increased risk for metabolic diseases.
How to Get Accurate Measurements
For the most accurate results from this calculator, follow these measurement tips:
Neck: Measure just below the larynx, keeping the tape horizontal.
Waist: For men, measure at the navel. For women, measure at the narrowest part of the torso.
Hips (Women only): Measure at the widest point of the buttocks.
Consistency: Always measure at the same time of day, preferably in the morning before eating or exercising.
Example Calculation
Consider a male who is 70 inches tall, with a 16-inch neck and a 36-inch waist. Using the Navy formula:
Result: 20.4% Body Fat (Category: Average).
This individual would know that while they are in the healthy "Average" range, they might aim for a waist reduction or muscle increase to move into the "Fitness" category.