Body Fat Calculator
Estimate body fat % (U.S. Navy method)
Estimate your body fat percentage with the U.S. Navy tape method — just a few measurements and no special equipment.
How the Navy method works
The US Navy circumference method estimates body fat from a handful of tape measurements. It works because the ratio of waist to neck (and hips for women) tracks how much fat you carry relative to your frame — no calipers, scanner or scale required.
Men: 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
Women: 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
An estimate, not a clinical measurement. DEXA, hydrostatic weighing and BodPod are the reference methods. Nothing here is medical advice.
Taking the measurements
| Measurement | Where | Notes |
|---|---|---|
| Neck | Just below the larynx | Tape sloping slightly down at the front |
| Waist (men) | At the navel | Relaxed, at the end of a normal breath out |
| Waist (women) | At the narrowest point | Usually above the navel |
| Hips (women) | At the widest point | Feet together |
| Height | Without shoes |
- Do not suck in. Breathe out normally and let the tape sit where the body is.
- Keep the tape level all the way round and snug without compressing the skin.
- Measure twice and average. If the two differ by more than a quarter inch, measure again.
- Same time of day, every time. Mornings before eating are the most consistent.
How sensitive the estimate is to the tape
| Waist | Estimated body fat |
|---|---|
| 30″ | 8.7% |
| 32″ | 13.4% |
| 34″ | 17.5% |
| 36″ | 21.3% |
| 38″ | 24.6% |
| 40″ | 27.8% |
Two inches of waist moves the estimate by roughly 4 percentage points. That is the single most important thing to understand about this method: sloppy tape placement produces a bigger swing than months of real progress. Half an inch of measurement error is about one point of body fat.
This is why the method is far better at tracking change than at pinning down an absolute number. If you measure the same way every time, a downward trend is real even if the absolute figure is a couple of points off.
Typical ranges
| Category | Men | Women |
|---|---|---|
| Essential fat | 2 to 5% | 10 to 13% |
| Athletes | 6 to 13% | 14 to 20% |
| Fitness | 14 to 17% | 21 to 24% |
| Acceptable | 18 to 24% | 25 to 31% |
| Above average | 25% and over | 32% and over |
Women carry more essential fat than men for physiological reasons, which is why the ranges differ by roughly ten points throughout. Both sets drift upward with age at equivalent health.
Accuracy, honestly
Studies generally place the Navy method within about 3 to 4 percentage points of DEXA for most people, which is respectable for a tape measure and useless for precision claims. Where it drifts furthest:
- Very lean or very heavy people, at both ends of the range the equation was fitted on.
- Very muscular builds, where a thick waist is partly muscle and reads as fat.
- Unusual fat distribution, since the method infers everything from a few circumferences.
- Inconsistent measuring, which dominates all of the above.
Compared with BMI, this is a meaningful step forward: BMI cannot separate muscle from fat at all, while the Navy method at least uses waist relative to frame and so captures abdominal fat. Neither replaces a scan, and both are most useful as trends.
How this body fat calculator works out its numbers
Uses the US Navy circumference method in inches. Men: 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76. Women: 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387.
- Estimation, not measurement. DEXA, hydrostatic weighing and air displacement are the reference methods; this is a regression fitted to circumference data.
- Typically within 3 to 4 percentage points of DEXA for people near the middle of the range the equation was derived from, with larger error at the extremes and for very muscular builds.
- Highly sensitive to tape placement. Two inches of waist shifts the result about 4 points, so measurement consistency matters more than any other factor. Use it for trends.
- Adults only, and not applicable during pregnancy.
- Not medical advice. Reference ranges are common fitness-industry conventions rather than clinical thresholds.
Reviewed September 2026.
Figures reviewed . Every worked example on this page is checked against the calculator above.
Body Fat Calculator: frequently asked questions
How does the Navy body fat method work?
It estimates body fat from the ratio of waist to neck, plus hips for women, against height. The logarithmic formula was derived from US Navy data and needs only a tape measure.
What's a healthy body fat percentage?
Roughly 14 to 17% for men and 21 to 24% for women is the commonly cited fitness range, with 18 to 24% and 25 to 31% considered acceptable. Women carry about ten points more essential fat for physiological reasons.
How accurate is the Navy method?
Within about 3 to 4 percentage points of a DEXA scan for most people. It drifts furthest for very lean, very heavy or very muscular builds, and it is much better at tracking change than at fixing an absolute number.
Where do I measure my waist for body fat?
Men measure at the navel; women at the narrowest point, usually above the navel. Breathe out normally, do not suck in, keep the tape level and snug without compressing the skin.
How much does measurement error matter?
A great deal. On a 70-inch man, two inches of waist changes the estimate by about 4 percentage points, so half an inch of tape error is roughly one point of body fat — larger than months of genuine progress.
What's the difference between BMI and body fat percentage?
BMI uses only height and weight and cannot tell muscle from fat. Body fat percentage estimates how much of your weight is fat, so two people with the same BMI can differ substantially. Neither replaces a clinical measurement.
Why do men and women use different formulas?
Because fat distribution differs systematically, so women's measurement includes hip circumference. The essential fat ranges also differ by around ten percentage points, which is physiological rather than a fitness gap.
How often should I measure?
Every two to four weeks is enough. Measuring more often mostly captures day-to-day variation in bloating and hydration rather than change in body composition.