Body Fat Percent Calculator

U.S. Navy Body Fat Percentage Calculator

Male Female

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function toggleHipInput() { var gender = document.getElementById('bf_gender').value; var hipBox = document.getElementById('hip_container'); if (gender === 'female') { hipBox.style.display = 'block'; } else { hipBox.style.display = 'none'; } } function calculateBF() { var gender = document.getElementById('bf_gender').value; var height = parseFloat(document.getElementById('bf_height').value); var neck = parseFloat(document.getElementById('bf_neck').value); var waist = parseFloat(document.getElementById('bf_waist').value); var resultDiv = document.getElementById('bf_result_area'); var resultVal = document.getElementById('bf_percentage'); var resultCat = document.getElementById('bf_category'); if (!height || !neck || !waist || (gender === 'female' && !document.getElementById('bf_hips').value)) { alert("Please fill in all measurements."); return; } var bodyFat = 0; if (gender === 'male') { // Navy Method for Men: 495 / (1.0324 – 0.19077 * log10(waist – neck) + 0.15456 * log10(height)) – 450 var logWaistNeck = Math.log10(waist – neck); var logHeight = Math.log10(height); bodyFat = 495 / (1.0324 – (0.19077 * logWaistNeck) + (0.15456 * logHeight)) – 450; } else { // Navy Method for Women: 495 / (1.29579 – 0.35004 * log10(waist + hip – neck) + 0.22100 * log10(height)) – 450 var hips = parseFloat(document.getElementById('bf_hips').value); var logWaistHipNeck = Math.log10(waist + hips – neck); var logHeightF = Math.log10(height); bodyFat = 495 / (1.29579 – (0.35004 * logWaistHipNeck) + (0.22100 * logHeightF)) – 450; } if (bodyFat > 0 && bodyFat < 100) { resultVal.innerHTML = bodyFat.toFixed(1) + "%"; resultDiv.style.display = 'block'; var category = ""; if (gender === 'male') { if (bodyFat < 6) category = "Essential Fat"; else if (bodyFat < 14) category = "Athletic"; 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 = "Athletic"; else if (bodyFat < 25) category = "Fitness"; else if (bodyFat < 32) category = "Average"; else category = "Obese"; } resultCat.innerHTML = "Category: " + category; } else { alert("Please check your measurements. The logic produced an impossible result."); } }

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Body fat percentage is a much more accurate health marker than total weight or Body Mass Index (BMI). While BMI only looks at your weight relative to your height, body fat percentage distinguishes between "lean mass" (muscle, bone, water) and "fat mass." This calculator uses the U.S. Navy Method, a widely accepted formula for estimating body composition without expensive clinical equipment like DEXA scans or hydrostatic weighing.

How the U.S. Navy Body Fat Formula Works

The U.S. Navy developed this method to provide an accessible way to measure the fitness levels of personnel. The formula relies on specific circumference measurements that correlate strongly with body fat levels:

• Height: Used as the baseline for body proportions.
• Neck: Helps differentiate between lean mass in the upper body and fat storage.
• Waist: The primary location for abdominal (visceral) fat storage.
• Hips (Women only): Since women naturally carry more fat in the pelvic region for reproductive health, this measurement is crucial for accuracy in female calculations.

Body Fat Categories for Men and Women

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%+

Calculation Example: Male Athlete

Consider a man who is 180 cm tall, with a 39 cm neck and a 84 cm waist. Using the Navy formula:

Log10(84 – 39) = 1.653
Log10(180) = 2.255
Body Fat % ≈ 13.8% (Athletic/Fitness Category)

Calculation Example: Female Fitness

Consider a woman who is 165 cm tall, with a 34 cm neck, 72 cm waist, and 94 cm hips:

Log10(72 + 94 – 34) = 2.120
Log10(165) = 2.217
Body Fat % ≈ 22.4% (Fitness Category)

Frequently Asked Questions

Is this as accurate as a DEXA scan?
While the Navy Method is surprisingly accurate for most people (usually within 3-4%), it cannot account for specific muscle density. For elite bodybuilders or those with unusual body types, clinical methods are preferred.

When should I take my measurements?
For the most consistent results, measure yourself in the morning before eating or exercising. Ensure the measuring tape is snug against the skin but not compressing the tissue.

Why does my body fat percentage fluctuate?
Hydration levels can affect your waist measurement slightly, and sodium intake can cause water retention in the abdominal area. Aim for weekly or monthly trends rather than daily tracking.