Body Fat Calculator
Estimate your body-fat percentage from a few tape measurements using the US Navy method (metric, in centimetres).
Estimated from a single tape measurement, so treat it as a ballpark within a few points of a body scan.
A man 178 cm tall with a 38 cm neck and 85 cm waist has about 16.4% body fat by the US Navy method: 495 ÷ (1.0324 − 0.19077·log₁₀(85 − 38) + 0.15456·log₁₀(178)) − 450 ≈ 16.4%. That places him in the fitness range for men.
What the US Navy method does
The US Navy tape method estimates body-fat percentage from body circumferences instead of skinfold calipers or a scan. It relies on the fact that fat and lean tissue are distributed in predictable places: for men the ratio of waist to neck (scaled by height) tracks body fat well, and for women the hip measurement is added because fat storage patterns differ. You only need a flexible tape measure and a wall for height.
Because it uses just a few measurements, it is quick and repeatable, but it is a statistical estimate — it infers fat from shape rather than measuring it directly, so it works best for tracking change over time on the same body.
Women: %BF = 495 ÷ (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height)) − 450. All measurements in centimetres; log₁₀ is base-10.
Worked example: man, 178 cm tall, 38 cm neck, 85 cm waist
Put the tape figures into the men’s formula, in centimetres:
- 1 Choose your sex. Men and women use different constants, and women also need a hip measurement.
- 2 Measure your neck. Wrap the tape just below the larynx (Adam’s apple), sloping slightly down toward the front. Example: 38 cm.
- 3 Measure your waist. Men measure at the navel; women measure at the narrowest point. Keep the tape level and relax your stomach. Example: 85 cm.
- 4 Women: measure the hips. Measure around the widest part of the buttocks, tape parallel to the floor. Skip this step for men.
- 5 Measure your height. Stand against a wall without shoes. Example: 178 cm.
- 6 Read the result. 495 ÷ (1.0324 − 0.19077·log₁₀(85 − 38) + 0.15456·log₁₀(178)) − 450 ≈ 16.4%, which is the fitness range for men.
Body-fat categories (ACE ranges)
American Council on Exercise descriptive ranges. Women naturally carry more essential fat than men.
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25% and up | 32% and up |
How to read your number
Where you land in these bands matters more than the exact decimal. Essential fat is the minimum needed for normal function; dropping below it is unhealthy. The athlete and fitness bands reflect visibly lean, active bodies, while the average band covers most of the population. The same person can shift a point or two between readings just from tape placement, breathing, or hydration, so re-measure the same way each time and watch the trend.
This tool is for general information, not medical advice. The tape method carries a margin of error of roughly ±3–4 percentage points versus a lab scan, so use it to track change rather than as a clinical diagnosis, and consult a qualified professional about your health.