Body Fat Calculator

The US Navy Body Fat Method Explained

The US Navy circumference method estimates body fat percentage from body measurements rather than weight alone. Developed by Hodgdon and Beckett in 1984, it's used by military branches worldwide for fitness assessments. For men, it uses waist and neck circumference; for women, it adds hip circumference to the equation.

Men: BF% = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76

Women: BF% = 163.205 × log10(waist + hips − neck) − 97.684 × log10(height) − 78.387

All measurements are in inches. The formula has a margin of error of roughly ±3–4 percentage points versus DEXA scans, which is acceptable for most fitness tracking purposes.

Body Fat Categories for Men and Women

Men:

• Essential Fat: 2–5%
• Athletic: 6–13%
• Fitness: 14–17%
• Average: 18–24%
• Obese: 25%+

Women:

• Essential Fat: 10–13%
• Athletic: 14–20%
• Fitness: 21–24%
• Average: 25–31%
• Obese: 32%+

Women naturally carry more body fat than men due to hormonal and reproductive differences — this is healthy and expected. Essential fat is the minimum required for basic physiological function.

Healthy Body Fat by Age

Body fat percentage tends to increase naturally with age even as weight stays the same, partly due to muscle loss (sarcopenia). These are healthy ranges by decade:

• 20–39: Men 8–19%, Women 21–32%
• 40–59: Men 11–21%, Women 23–33%
• 60+: Men 13–24%, Women 24–35%

How to Measure Accurately

Measurement technique matters — a sloppy tape can throw your results off by 3–5%:

• Waist (men): Measure at the narrowest point, usually around the navel. Don't suck in.
• Waist (women): Same as men — narrowest horizontal point of the torso.
• Neck: Below the larynx (Adam's apple), tape slightly downward toward the front.
• Hips (women): Widest point of the hips/buttocks.
• Measure first thing in the morning before eating for the most consistent results.
• Keep the tape snug but not compressing the skin.

Comparing Body Fat Methods

• Navy Method (this calculator): ±3–4% error, free, no equipment needed
• DEXA Scan: ±1–2% error, gold standard, costs $50–150, requires a clinic visit
• Hydrostatic Weighing: ±1–2% error, very accurate, rare and inconvenient
• Skinfold Calipers: ±3–5% error, cheap, technique-dependent
• BIA (bioelectrical impedance): ±3–8% error, affected by hydration, widely available

For most people, the Navy method is accurate enough to track progress. Use it consistently to monitor trends over time rather than obsessing over the absolute number.

How to Reduce Body Fat

Body fat reduction comes down to a caloric deficit — burning more than you consume. But the strategy matters:

• Moderate deficit (300–500 cal/day): Lose ~0.5–1 lb/week, preserves more muscle
• Strength training: Builds muscle while losing fat, improves body composition independent of weight
• High protein (0.7–1g per lb of body weight): Preserves lean mass during a cut
• Sleep 7–9 hours: Poor sleep raises cortisol, increases fat storage
• Cardio: Effective for fat loss, but diet does most of the work

Frequently Asked Questions

Is this calculator accurate? Within ±3–4% versus DEXA scans in most cases. It's more accurate for people with typical body proportions and less accurate for very muscular or very obese individuals.

Why do I weigh the same but look different? You may have gained muscle while losing fat — a process called body recomposition. This is why body fat percentage is a better health indicator than weight alone.

What's the lowest healthy body fat for men/women? For men, around 5–6% (below essential fat is dangerous). For women, around 13–14%. Going below these levels impairs hormone function and organ health.