Body Fat Calculator
Enter your height, neck, and waist (plus hip if you're female) to estimate body fat percentage with the U.S. Navy circumference method — a tape-measure formula developed for military fitness testing. It needs no calipers, scale, or scan, and lands within roughly ±3-4 percentage points of underwater-weighing results for most adults.
Your measurements
Results
Estimated body fat
28.6
% body fat
U.S. Navy circumference method — accurate to roughly ±3-4%
Formula applied
163.205×log10(55.0) − 97.684×log10(65.0) − 78.387 = 28.6%
- Method
- U.S. Navy circumference
- Typical error margin
- ±3-4 percentage points
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Save this to my planHow to take accurate measurements
This calculator is only as good as the tape measurements that go into it. Use a flexible cloth or vinyl tape, keep it parallel to the floor, and pull it snug against the skin without compressing soft tissue.
Neck: measure just below the larynx (Adam's apple), with the tape angled slightly downward toward the front of the neck.Waist: measure at the navel, not at your shirt's waistband or the narrowest point of your torso — the Navy formula was built around the navel measurement specifically.Hip (women only): measure around the widest point of your glutes and hips, standing with feet together. Take each measurement two or three times and use the average to reduce error from tape tension or posture.
What body fat percentage ranges typically mean
These ranges are general reference points commonly published for context, not diagnostic thresholds — where you fall depends on your goals, training history, and how your body carries fat, not just the category label.
| Category | Women | Men |
|---|---|---|
| Essential fat | 10-13% | 2-5% |
| Athletes | 14-20% | 6-13% |
| Fitness | 21-24% | 14-17% |
| Average | 25-31% | 18-24% |
| Obese | 32%+ | 25%+ |
Given the method's ±3-4 percentage point error margin, use your result to place yourself in a general range rather than to chase an exact figure — and re-measure every few weeks to track the trend, which is more reliable than any single reading.
Frequently asked questions
How accurate is the Navy method compared to DEXA or underwater weighing?
It's an estimate, not a lab measurement. Validated against underwater weighing, the Navy circumference method typically lands within about ±3-4 percentage points of a person's true body fat. DEXA and hydrostatic weighing are more precise, but the Navy method needs only a tape measure, which makes it useful for tracking change over time rather than getting an exact number.
How do I measure my waist, neck, and hip correctly?
Measure your neck just below the larynx (Adam's apple), angled slightly downward at the front. Measure your waist at the navel, not at the narrowest point of your torso. Measure hips at the widest point around your glutes. Keep the tape snug against the skin but not compressing it, and take each measurement two or three times to make sure the numbers agree.
Why does the calculator ask for different measurements for men and women?
The underlying formulas were derived separately for each sex because body fat distributes differently between men and women — women typically carry more fat around the hips, so the female equation adds a hip measurement that the male equation does not need. Using the wrong equation for your sex will produce an inaccurate result.
How often should I re-measure to track progress?
Every 2-4 weeks is enough to see a real trend without chasing day-to-day noise from water retention, food volume, or measurement inconsistency. Take measurements at the same time of day, ideally in the morning before eating, and compare the trend across several readings rather than reacting to any single number.
Can I use this method if I have an athletic or unusual build?
The Navy method can lose accuracy for people with very high muscle mass or an atypical waist-to-hip ratio, since it was derived from average body proportions in a military population. If that describes you, treat the result as a rough estimate and lean more heavily on the trend over time than the absolute number.
Sources
- Prediction of Percent Body Fat for U.S. Navy Men from Body Circumferences and Height — Hodgdon JA, Beckett MB — Naval Health Research Center, Report No. 84-11 (accessed August 2026)
- Prediction of Percent Body Fat for U.S. Navy Women from Body Circumferences and Height — Hodgdon JA, Beckett MB — Naval Health Research Center, Report No. 84-29 (accessed August 2026)