Body Fat Calculator (US Navy Method)
Enter sex, age, height, weight, and tape measurements on the left; the body fat percentage updates instantly on the right, with your position on the category axis below.
Input
Results update automatically as you type.
Result
- Fat mass
- —
- Lean mass
- —
- BMI
- —
- BMR
- —
Body fat categories by sex
Axis ticks are the category boundaries for the selected sex; the dot is your current value. Categories follow common ACE-style conventions.
Tape-based estimates can vary 1–3 points with measurement position and posture, and are not a medical diagnosis. Pregnancy or high muscle mass can shift results.
ready to use.
- Visible firstKeep the input and result positions clear.
- Results firstPut the main number up front and keep the process secondary.
- Less to askNo sign-up or extra information before using the tool.
Estimating body fat with nothing but a tape measure
Body fat percentage is the share of your weight that is fat. This calculator uses the US Navy circumference method: waist and neck (plus hip for women) girths and height go into a logarithmic formula, and combined with weight the result splits into fat mass and lean mass.
The tape method is a practical estimate — it needs only a tape measure — but position and posture can move it by 1–3 points. Treat it as a trend tool, not a replacement for precise methods such as DEXA.
The US Navy formula: a logarithmic tape method
Men use waist minus neck; women use waist plus hip minus neck, together with height. It was built for fast large-scale screening in the military and is still used for fitness standards.
- Men: 495 ÷ (1.0324 − 0.19077×log10(waist−neck) + 0.15456×log10(height)) − 450
- Women: 495 ÷ (1.29579 − 0.35004×log10(waist+hip−neck) + 0.221×log10(height)) − 450
- All lengths in cm internally; unit switching converts automatically
Screen flow: input, percentage, category axis
Change any value on the left and the right panel recalculates without a button. On the axis below, the dot shows where you sit between the boundary ticks for your sex, and the highlighted category card gives the label.
Where you place the tape decides the number
The same person measures differently at different spots.
- Waist: horizontally at navel height, relaxed
- Neck: just below the larynx, tape sloped slightly forward
- Hip (women): around the widest point
- Measure after exhaling, without compressing the skin
Categories differ by sex
Women carry more essential fat for physiological functions, so every band sits higher.
- Men: essential 2–5 · athlete 6–13 · fitness 14–17 · average 18–24 · obese 25%+
- Women: essential 10–13 · athlete 14–20 · fitness 21–24 · average 25–31 · obese 32%+
- Bands follow common ACE-style conventions, not a medical standard
Male example: 5'9" · 160 lb · waist 34" · neck 15"
The default profile on the English page, converted to metric internally.
- Waist − neck
- 86.4 − 38.1 = 48.3 cm
- Body fat
- about 17.9% (Average)
- Fat mass
- 160 × 0.179 ≈ 28.6 lb
- Lean mass
- 160 − 28.6 ≈ 131.4 lb
Female example: 5'4" · 130 lb · waist 28" · neck 12.5" · hip 38"
The sample button applies this profile.
- Waist + hip − neck
- 71.1 + 96.5 − 31.8 = 135.9 cm
- Body fat
- about 27.0% (Average)
- Fat mass
- 130 × 0.270 ≈ 35.1 lb
- BMR
- about 1,305 kcal/day (Mifflin)
Read fat mass and lean mass separately
Weight-loss goals are usually fat-loss goals. At the same body weight, gaining lean mass (muscle, bone, water) while losing fat is an improvement. The BMI and BMR cards are companion outputs from the same inputs.
Know the limits of the tape method
This estimate is a statistical model.
- High muscle mass tends to be overestimated
- Do not use during pregnancy, edema, or medical conditions
- Absolute values differ from device measurements (BIA, DEXA); track trends with one method
- This page is an educational tool, not medical advice
Body fat FAQ
Which formula does this calculator use?
The US Navy circumference method: waist minus neck for men, waist plus hip minus neck for women, with height, in a logarithmic formula. Its advantage is that it needs only a tape measure.
Why does it differ from my smart scale?
Different methods. The tape method is a statistical formula, smart scales use bioelectrical impedance, and DEXA uses X-ray absorption. Absolute differences are normal; compare trends within one method.
Where exactly do I measure?
Waist horizontally at navel height, neck just below the larynx, and for women the widest point of the hips. Measure after exhaling without compressing the skin.
Can I enter pounds and inches?
Yes — the English page defaults to lb · ft/in: weight in pounds, height in feet and inches, girths in inches, converted internally. Fat and lean mass are shown in your selected units.
What are the category bands based on?
Common ACE-style conventions: for men essential 2–5%, athlete 6–13%, fitness 14–17%, average 18–24%, obese 25%+; each band sits higher for women. They are not a medical diagnostic standard.
Reviewed: 2026-07-11. Category bands are conventions, not a medical standard.