How this body fat calculator works
Your body fat percentage is the proportion of your total weight that is fat, with the rest being lean mass — muscle, bone, organs and water. It is a more useful picture of body composition than weight alone, because two people of the same weight can carry very different amounts of fat.
This tool uses the U.S. Navy circumference method, which estimates body fat from tape measurements rather than weight. For men it combines the difference between the waist and neck with your height; for women it adds the hip measurement. The numbers are fed into a base-10 logarithmic equation:
Men: %BF = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450. Women: %BF = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450. All measurements are in centimetres (imperial inches are multiplied by 2.54 first).
Reference note: if you enter your weight, fat mass is body fat percentage × weight and lean mass is the remainder. The method needs your waist to be larger than your neck (and, for women, waist + hip larger than neck), or the formula has no valid result.
How to measure
Use a flexible tape on bare skin, snug but not compressing. Measure two or three times and average:
| Measurement | Where to measure |
|---|---|
| Neck | Just below the larynx, tape sloping slightly down at the front |
| Waist (men) | Horizontally at the navel, relaxed (do not suck in) |
| Waist (women) | Horizontally at the narrowest point of the torso |
| Hip (women) | Horizontally at the widest point of the hips and buttocks |
Frequently asked questions
- How is body fat percentage measured?
- Body fat percentage is the share of your total weight that is fat. It can be measured directly with DEXA scans, underwater weighing or skinfold calipers. This tool uses the U.S. Navy circumference method, which estimates body fat from tape measurements of your neck, waist, height and — for women — hips, so all you need is a measuring tape.
- What is the U.S. Navy body fat method?
- It is a formula from the Naval Health Research Center that estimates body fat from circumference measurements rather than weight. For men it uses waist minus neck plus height; for women it adds the hip measurement. The values are combined with base-10 logarithms in an equation the U.S. armed forces use to screen body composition.
- What is a healthy body fat percentage?
- Healthy ranges differ by sex. Using ACE-style categories, men fall around 14–17% for fitness and 18–24% for average, while women run about 21–24% for fitness and 25–31% for average. Essential fat is roughly 2–5% for men and 10–13% for women. These are general guidelines, not medical thresholds.
- How accurate is the Navy body fat calculator?
- The Navy method is a quick, low-cost estimate, typically within about 3–4 percentage points of a clinical measurement for most people. Accuracy depends on measuring consistently and in the right spots. It is a screening estimate, not a diagnosis — for precise results use a DEXA scan or other clinical method.
- How do I measure my waist and neck correctly?
- Use a flexible tape held snug but not compressing, on bare skin, standing relaxed. Measure the neck just below the larynx with the tape sloping slightly down at the front. Measure the waist horizontally at the navel for men and at the narrowest point for women; women also measure hips at the widest point. Average two or three readings.
- Should I see a professional about my body fat?
- Yes if you have concerns. This calculator is an educational estimate and does not provide diagnosis or treatment. These figures are informational and not medical advice — if you are planning major weight changes or have a health condition, consult a qualified doctor, dietitian or other health professional before acting on any number here.