CalcVitalsBody Fat Percentage Calculator
The US Navy tape method estimates body fat from waist, neck and height. For example, a man with an 85 cm waist, 38 cm neck and 175 cm height gets 17.0%. It needs only a tape measure and lands within a few points of laboratory methods for most people.
How it works
Body fat percentage answers the question BMI cannot: of the weight you carry, how much is fat and how much is everything else? The US Navy method was developed for exactly the situation most people are in — no laboratory, just a tape measure. It works because waist and neck circumferences track the body's fat stores closely enough that a logarithmic formula fitted against underwater weighing can recover a useful estimate.
Technique matters more than arithmetic. Measure the waist horizontally at the level of the navel, at the end of a normal breath out, with the tape snug but not denting the skin. The neck goes just below the Adam's apple, tape angled slightly downward toward the front. Women add the hips at their widest point. Take each measurement twice and average if they disagree.
The BMI-based alternative (Deurenberg) needs no tape at all — it infers body fat from BMI, age and sex — but it inherits every weakness of BMI and adds an age drift, so treat it as the rougher of the two. Either way, the trend across months, measured the same way each time, is worth far more than any single reading.
The method
US Navy (Hodgdon) circumference method: for men, BF% = 86.010·log₁₀(waist − neck) − 70.041·log₁₀(height) + 36.76; for women, BF% = 163.205·log₁₀(waist + hip − neck) − 97.684·log₁₀(height) − 78.387 — with all measurements in inches; centimetre entries are converted first (1 in = 2.54 cm exactly). BMI method: Deurenberg BF% = 1.20·BMI + 0.23·age − 10.8·sex (male = 1) − 5.4. Categories follow the American Council on Exercise bands.
Frequently asked questions
How accurate is the Navy method?
Against laboratory references it is usually within about 3–4 percentage points for most adults — good enough to track change over time, not good enough to argue over a single point. Consistent measuring technique matters more than the formula.
What is a healthy body fat percentage?
Broadly: men 14–24% covers the fit-to-average range, women 21–31%, reflecting the higher essential fat women carry. Athletes sit lower; essential fat is roughly 2–5% for men and 10–13% for women, and going near it is neither safe nor sustainable.
Where exactly do I measure my waist?
Horizontally at the level of your navel, standing relaxed, at the end of a normal exhale. Not at the narrowest point of the torso, not sucked in, and not over clothing.
Why do the two methods disagree?
They measure different things. The Navy method reads your actual circumferences; the Deurenberg method guesses body fat from BMI and age, so it cannot see a muscular build or an unusual fat distribution. When they disagree, trust the tape — measured carefully.