About this calculator
Two people with the same weight and the same BMI can have completely different bodies — one muscular, one not. Body fat percentage measures what BMI cannot: how much of you is fat versus everything else (muscle, bone, water, organs). It is the better compass for fitness goals, because losing five pounds of fat and gaining five pounds of muscle is progress that a scale alone calls nothing.
The US Navy method estimates body fat from circumference measurements. It was designed to assess thousands of service members cheaply, and validation studies put it within about 3–4 percentage points of underwater weighing for most people — remarkable for a tape measure, and plenty accurate for tracking change over time.
How to use it
- Measure with a flexible tape, snug against the skin without compressing it, ideally in the morning.
- Neck: just below the larynx (Adam's apple), tape sloping slightly down to the front.
- Waist: horizontal at the navel, after a normal breath out — do not suck in. Hips (women): the widest point.
- Enter measurements and your weight to also get fat mass and lean mass.
The formula
All measurements in inches. The formulas rest on a reliable pattern: fat accumulates at the waist (and hips) far more than at the neck, so the gaps between those circumferences, scaled by height, predict total body fat.
Worked example
A man 70 in tall with a 36 in waist and 15 in neck: 86.010 × log₁₀(21) − 70.041 × log₁₀(70) + 36.76 ≈ 21.3% body fat — the "average" band. At 190 lb that is about 40.5 lb of fat mass and 149.5 lb of lean mass. A woman 65 in tall with 30 in waist, 38 in hips and 13 in neck measures about 28.6%, also in the average band for women (who naturally carry more essential fat).
Frequently asked questions
What is a healthy body fat percentage?
For men, roughly 14%–24% covers the fitness-to-average span, with athletes at 6%–13% and obesity starting around 25%. For women the healthy span is higher — athletes 14%–20%, fitness 21%–24%, average 25%–31%, obesity from about 32% — because women carry essential fat (roughly 10%–13%) that men (2%–5%) do not.
How accurate is the Navy method compared with DEXA or calipers?
DEXA scans are the practical gold standard; the Navy method typically lands within ±3–4 points of reference methods, calipers within ±3–5 in skilled hands. For tracking your own progress, consistency of measurement technique matters more than the method chosen — measure the same way, at the same time of day.
Where exactly do I measure my waist?
At the navel (belly button), horizontally around the body, standing relaxed after breathing out normally. Not at the narrowest point of the torso, not at the belt line, and never pulled tight. This is also the waist measure used in medical waist-circumference guidelines.
Why does the women's formula include hips?
Because fat distribution differs by sex: women store proportionally more fat in the hips and thighs (gluteofemoral fat), so waist alone underestimates total body fat. Including the hip circumference captures that depot and makes the estimate comparable in accuracy to the men's version.