📝 Measurement Instructions:

• Neck: Measure below larynx (Adam's apple), tape snug but not compressing[web:150]
• Waist (Men): At belly button level, horizontally around abdomen[web:150]
• Waist (Women): At narrowest point, usually above navel[web:150]
• Hip (Women only): At widest point of buttocks[web:150]

🔬 Navy Method

Uses circumference measurements (neck, waist, hip, height)[web:144][web:147]

Accuracy: ±3-4%, practical for home use

📐 Better Than BMI

Distinguishes muscle from fat, unlike BMI[web:144]

Important for athletes and fitness enthusiasts

🎯 Health Indicator

Correlates with cardiovascular health and metabolic risk[web:148]

More accurate than weight alone

👨 Men

Source: American Council on Exercise[web:151]

👩 Women

Source: American Council on Exercise[web:151]

Formula 1: U.S. Navy Method for Men

Calculate body fat percentage using circumference measurements:[web:144]

\[\%BF = \frac{495}{1.0324 - 0.19077 \times \log_{10}(W - N) + 0.15456 \times \log_{10}(H)} - 450\]

Where \(W\) = waist (cm), \(N\) = neck (cm), \(H\) = height (cm)

Formula 2: U.S. Navy Method for Women

Women's formula includes hip measurement:[web:144]

\[\%BF = \frac{495}{1.29579 - 0.35004 \times \log_{10}(W + H_p - N) + 0.22100 \times \log_{10}(H)} - 450\]

Where \(W\) = waist (cm), \(H_p\) = hip (cm), \(N\) = neck (cm), \(H\) = height (cm)

Formula 3: Fat Mass Calculation

Calculate total fat mass from body fat percentage:

\[FM = BW \times \frac{\%BF}{100}\]

Where \(FM\) = fat mass, \(BW\) = body weight, \(\%BF\) = body fat percentage

Formula 4: Lean Body Mass (LBM)

Calculate lean mass (muscles, bones, organs):

\[LBM = BW - FM = BW \times \left(1 - \frac{\%BF}{100}\right)\]

Lean body mass is everything except body fat.

Formula 5: BMI Calculation

Body Mass Index for comparison:[web:158]

\[BMI = \frac{W_{\text{kg}}}{H_{\text{m}}^2}\]

Weight in kilograms divided by height in meters squared.

Formula 6: Body Fat to Lose/Gain

Calculate weight change needed to reach goal:

\[\Delta W = \frac{LBM}{\left(1 - \frac{\%BF_{\text{goal}}}{100}\right)} - BW\]

Positive = need to gain, negative = need to lose weight.

❤️ Cardiovascular Health

Excess body fat, especially around the waist, increases risk of heart disease, high blood pressure, and stroke. Maintaining healthy levels improves cardiovascular function and longevity.[web:148]

⚡ Metabolic Function

Body fat influences insulin sensitivity, glucose metabolism, and diabetes risk. Healthy body composition supports balanced blood sugar and efficient energy use.[web:148]

🏋️ Athletic Performance

Athletes optimize body fat for performance. Too little impairs performance and health, while optimal levels enhance power-to-weight ratio, endurance, and recovery.[web:148][web:151]

🧪 Hormone Balance

Body fat plays crucial roles in hormone production. Too little disrupts reproductive hormones and metabolism, while excess fat increases estrogen levels and inflammation.[web:148]

💪 Muscle Visibility

For aesthetic goals, body fat percentage determines muscle definition. Men typically need 10-12% to see abs, women 16-19%. Fitness enthusiasts track BF% for physique goals.[web:151]

🎯 Better Than BMI

BMI doesn't distinguish muscle from fat, often misclassifying muscular individuals as overweight. Body fat percentage provides accurate assessment of health regardless of muscle mass.[web:144][web:158]

💪 Women naturally have 6-11% more body fat than men due to reproductive functions and hormonal differences![web:151]

🔬 The Navy method was developed in the 1980s at the Naval Health Research Center in San Diego![web:144]

📊 Average body fat in the U.S. is about 28% for men and 40% for women—much higher than recommended![web:154]