Phase 6 · Biometric & Longevity

Body Fat Calculator (Navy Method)

A tape measure beats a bathroom scale. Use the U.S. Navy formula to estimate your body-fat percentage, category, and the split between fat mass and the lean mass you want to keep.

Educational estimate, not medical advice. The U.S. Navy circumference method approximates body-fat percentage from tape measurements — it is not a clinical measurement like DEXA or hydrostatic weighing, and it can drift for very lean or very muscular builds. Use it to track trends over time, not as a diagnosis, and consult a doctor about any health decisions.

How do you calculate body fat with the Navy method?

It uses circumference measurements and height, not weight. For men: 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76. For women, hip circumference is added to waist. Because it measures where fat is distributed rather than how much you weigh, it separates fat mass from the lean mass you want to keep.

Worked example (defaults on this page): a 5'10" man with a 34" waist and 15" neck at 180 lb estimates 17.5% body fat — about 31.5 lb of fat mass and 148.5 lb of lean mass.
Only the difference waist − neck drives the male result, which is why measuring technique matters more than precision: an inch of error at the waist moves the estimate by roughly 2 points.
Measure at the navel for waist and below the larynx for neck, relaxed, at the same time of day. Consistency between measurements matters more than absolute accuracy when tracking change.
It is an estimate, not a scan. DEXA and hydrostatic weighing are more accurate; the Navy method’s value is that it is free, repeatable and good at showing direction over weeks.

Under the hood

The math, fully exposed

The U.S. Navy (Hodgdon-Beckett) formula, using base-10 logs of your measurements in inches:

Men = 86.010 · log₁₀(waist − neck) − 70.041 · log₁₀(height) + 36.76

Women = 163.205 · log₁₀(waist + hip − neck) − 97.684 · log₁₀(height) − 78.387

Fat mass = bodyweight × body fat %

Lean mass = bodyweight − fat mass

It's circumference-based: the gap between waist and neck (and hip, for women) carries the signal — which is why measuring consistently matters more than absolute precision.
Lean mass is the number to protect: when dieting, watch that fat mass falls while lean mass holds — losing lean mass means losing muscle.
An estimate, not a scan: expect ±3–4 points versus DEXA; its value is tracking your trend over time.

Your directives

What to do next, based on your numbers

Adjust the sliders to generate tailored recommendations.

Answers

Frequently asked questions

How does the Navy body-fat method work?

Developed by the U.S. Naval Health Research Center, it estimates body fat from circumference measurements and height using a validated logarithmic formula. Men use neck and waist; women add the hip measurement. Because fat and muscle distribute differently around these sites, the ratios correlate well with overall body fat — giving a surprisingly good estimate from nothing but a tape measure.

How accurate is it compared to other methods?

For most people it lands within about 3–4 percentage points of a DEXA scan — less precise than DEXA or hydrostatic weighing, but far more accessible and more reliable than handheld bioimpedance gadgets. Its real strength is consistency: measure the same way each time and it tracks your trend accurately, which is what matters for seeing whether you are losing fat or muscle.

How do I measure correctly?

Use a flexible tape, snug but not compressing the skin, and measure relaxed (not sucking in). Neck: just below the larynx. Waist: at the navel for men, at the narrowest point for women. Hip (women): at the widest point. Take each measurement two or three times and average them — small errors in the tape translate into a few points of body fat, so consistency is everything.

What body-fat percentage should I aim for?

It depends on sex and goals. For men, ~6–13% is athletic, 14–17% fit, 18–24% average; for women, ~14–20% athletic, 21–24% fit, 25–31% average, reflecting essential fat differences. Going too low is unhealthy — below roughly 5% (men) or 12% (women) risks essential-fat loss. Aim for a sustainable range that supports performance and health, not the lowest possible number. This is an educational estimate, not medical advice.

Open the full Body Fat (Navy Method) calculator on EmpireCalc →