Calculate your estimated body fat percentage using common body measurements.
Male
Female
Your estimated body fat percentage will appear here.
Understanding Body Fat Percentage
Body fat percentage is a measure of the fat in your body relative to your total body weight. It's a more insightful health metric than simple weight or BMI, as it distinguishes between lean mass (muscle, bone, organs) and fat mass. Maintaining a healthy body fat percentage is crucial for overall health, affecting everything from hormone regulation and nutrient absorption to disease risk and physical performance.
This calculator utilizes common formulas derived from body measurements, which provide an estimation of body fat percentage. While these methods are convenient and accessible, they are not as precise as clinical methods like DEXA scans or hydrostatic weighing.
How the Calculation Works (Common Formulas)
There are several widely used formulas for estimating body fat percentage from circumference measurements. The specific formula used by this calculator adapts based on gender and input availability. A common approach for men involves height, waist, and neck measurements. For women, it typically includes height, waist, neck, and hip measurements.
General Principle: Larger circumferences relative to height often correlate with higher body fat. The formulas adjust for factors like bone density and muscle mass differences between genders.
Example Calculation (Illustrative):
Let's consider a 40-year-old male, weighing 85 kg, with a height of 180 cm, waist of 95 cm, and neck of 38 cm.
Step 1: Calculate Lean Body Mass (LBM) or Body Fat Percentage directly.
One common formula (US Navy Method) for men is:
BF% = 495 / (1.0324 - 0.19077 * log10(waist - neck) + 0.15456 * log10(height)) - 450
(Note: This is a simplified representation. Different formulas exist and may use age differently.)
For women, a similar formula exists but includes hip circumference and different constants:
BF% = 495 / (1.29579 - 0.35004 * log10(waist + hip - neck) + 0.22100 * log10(height)) - 450
Important Considerations:
Accuracy: This is an estimate. Measurement errors (e.g., incorrect tape tightness, measurement placement) significantly impact results.
Consistency: For tracking progress, always measure at the same time of day, under similar conditions, and using the same technique.
Individual Variation: Body composition varies greatly. Factors like genetics, fitness level, and overall health play a role.
Consult Professionals: For definitive body composition analysis and personalized health advice, consult a healthcare provider or a certified fitness professional.
Use this calculator as a tool for general awareness and motivation in your health journey.
function calculateBodyFat() {
var age = parseFloat(document.getElementById("age").value);
var gender = document.getElementById("gender").value;
var weightKg = parseFloat(document.getElementById("weightKg").value);
var heightCm = parseFloat(document.getElementById("heightCm").value);
var waistCm = parseFloat(document.getElementById("waistCm").value);
var neckCm = parseFloat(document.getElementById("neckCm").value);
var hipCm = parseFloat(document.getElementById("hipCm").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = 'Your estimated body fat percentage will appear here.';
if (isNaN(age) || isNaN(weightKg) || isNaN(heightCm) || isNaN(waistCm) || isNaN(neckCm)) {
resultDiv.innerHTML = "Please enter valid numbers for all required fields.";
return;
}
var bodyFatPercentage = 0;
if (gender === "male") {
if (isNaN(hipCm)) { // Hip is not strictly required for men in some formulas, but let's enforce it if entered.
hipCm = 0; // Default to 0 if not entered for men if formula requires it.
}
// US Navy Method for Men (simplified, typically uses waist, neck, height)
// BF% = 495 / (1.0324 – 0.19077 * log10(waist – neck) + 0.15456 * log10(height)) – 450
var logWaistNeck = Math.log10(waistCm – neckCm);
var logHeight = Math.log10(heightCm);
bodyFatPercentage = (495 / (1.0324 – 0.19077 * logWaistNeck + 0.15456 * logHeight)) – 450;
} else { // Female
if (isNaN(hipCm)) {
resultDiv.innerHTML = "Please enter your hip circumference for female calculation.";
return;
}
// US Navy Method for Women (simplified, uses waist, hip, neck, height)
// BF% = 495 / (1.29579 – 0.35004 * log10(waist + hip – neck) + 0.22100 * log10(height)) – 450
var logWaistHipNeck = Math.log10(waistCm + hipCm – neckCm);
var logHeight = Math.log10(heightCm);
bodyFatPercentage = (495 / (1.29579 – 0.35004 * logWaistHipNeck + 0.22100 * logHeight)) – 450;
}
// Basic validation for reasonable output
if (bodyFatPercentage 60) {
resultDiv.innerHTML = "Calculation resulted in an unusual value. Please check your measurements.";
} else {
resultDiv.innerHTML = "Estimated Body Fat: " + bodyFatPercentage.toFixed(1) + "%";
}
}
// Show/hide hip input based on gender selection
document.getElementById("gender").onchange = function() {
var gender = this.value;
var femaleHipInput = document.getElementById("female-hip-input");
if (gender === "female") {
femaleHipInput.style.display = "flex"; // Use flex to match input-group styling
} else {
femaleHipInput.style.display = "none";
// Clear hip input if switching from female to male
document.getElementById("hipCm").value = "";
}
};
// Trigger the onchange event once on load to set initial state correctly
document.getElementById("gender").dispatchEvent(new Event('change'));