Crunch Body Fat Calculator
BMI cannot tell muscle from fat; a tape measure does better. The US Navy method estimates body fat from circumferences — neck and waist (plus hips for women) against height — and this calculator adds your category, fat mass and lean mass.
Measure with a soft tape, snug but not compressing, standing relaxed. Men leave the hip field as-is — the male formula does not use it.
How it works
The Navy formulas use logarithms of circumferences: for men, body fat % = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76; for women, 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387 (all inches). Fat mass is weight × body fat %, and lean mass is everything else — the figure that matters if you are training, because it tells you whether the scale is moving the right tissue.
Formula & worked example
Formula: US Navy method, all measurements in inches. Men: body fat % = 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 = weight × body fat %; lean mass = weight − fat mass.
Worked example: A man 70 in tall with a 34 in waist and 15 in neck measures 17.51% body fat; at 180 lb that is 31.52 lb of fat mass and 148.48 lb of lean mass. A woman 65 in tall with a 30 in waist, 38 in hips and 13 in neck measures 28.56%.
Frequently asked questions
What is my body fat at a 34-inch waist and 15-inch neck?
For a man 5′10″ (70 in) tall: 17.5% — just over the top of the “Fitness” band, the first step into “Average”. At 180 lb that is 31.5 lb of fat mass and 148.5 lb of lean mass. Grow the neck or shrink the waist and the number moves fast, which is exactly what the formula is sensitive to.
What are healthy body fat ranges?
Commonly used bands for men: 2–5% essential, 6–13% athletes, 14–17% fitness, 18–24% average, 25%+ obese. For women: 10–13% essential, 14–20% athletes, 21–24% fitness, 25–31% average, 32%+ obese. Women carry more essential fat by physiology — the bands are not a double standard.
How accurate is the Navy method?
Against lab methods it is usually within roughly 3–4 percentage points when measurements are taken carefully — good enough to track change, not precise enough to argue over a single point. It beats BMI for anyone with real muscle, because it measures shape, not just weight.
Where exactly do I measure?
Neck: just below the Adam’s apple, tape angled slightly down. Waist: horizontal at the navel, after a normal exhale — not sucked in, not pushed out. Hips (women): the widest point of the buttocks. Same spots, same time of day, every time.
🥗 Feeding the lean mass?
The Macro Calculator turns a calorie target into daily protein, carb and fat grams — the numbers that decide what the lean mass does next.