Body Fat Calculator — US Navy Tape Method
Estimate your body fat percentage using the US Navy circumference formula — just a tape measure and a minute of your time. More useful than BMI because it actually tells you how much of your weight is fat versus lean mass.
📏 Estimate Your Body Fat %
Why Body Fat % Tells You More Than BMI
I have a friend, Marcus, who weighs 98 kg and is 6'1". His BMI puts him in the "overweight" category. His body fat is 11%. He's a competitive powerlifter with barely any fat on him. BMI would have you believe he needs to lose weight. Body fat percentage tells the actual story.
BMI only divides weight by height squared — it has absolutely no way to distinguish between fat and muscle tissue. Two people can have identical BMIs but completely different health profiles. Body fat percentage directly measures what actually matters for metabolic health: how much of your body weight is fat versus muscle, bone, and organs.
That said, body fat percentage isn't perfect either. What matters most is the trend — measuring consistently under the same conditions (same time of day, same hydration state) and tracking changes over months.
US Navy Body Fat Formula Explained
The US Navy developed this formula in the 1980s for practical field use — no expensive equipment, no lab setting, just a tape measure. It uses circumference measurements at specific body sites and height to estimate fat percentage.
For men: % BF = 86.010 × log₁₀(abdomen − neck) − 70.041 × log₁₀(height) + 36.76
For women: % BF = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
The error margin is roughly ±3–4% compared to DEXA scans. That's meaningful for absolute precision, but for month-to-month tracking it's more than adequate — and a lot cheaper than a DEXA scan every few weeks.
Body Fat Category Charts
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athlete | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Acceptable / Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
These ranges come from the American Council on Exercise (ACE). Women have higher healthy body fat ranges because of sex-specific hormonal and reproductive fat stores that are physiologically essential — not something to diet away.
How to Take Accurate Measurements
The biggest source of error in the Navy method isn't the formula — it's inconsistent measurements. Here's how to measure properly:
- Neck: Measure just below the larynx (Adam's apple), with the tape perpendicular to the neck. Keep your chin up and relaxed.
- Waist (men): At the navel. Exhale normally — don't suck in your stomach.
- Waist (women): At the narrowest point, usually about 1 inch above the navel.
- Hips (women only): At the widest point of the hips/buttocks, with feet together.
- Always measure first thing in the morning, before eating, in the same amount of clothing.
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