Body Fat Calculator
Estimate your body fat percentage using the US Navy tape-measure method from a few body circumference measurements.
Example
A man with waist 90 cm, neck 40 cm, height 180 cm:
495 / (1.0324 - 0.19077*log10(90-40) + 0.15456*log10(180)) - 450
= 495 / (1.0324 - 0.19077*1.69897 + 0.15456*2.25527) - 450
= 18.4% body fat -> category: Fitness
How it works
Pick your sex, then enter your height, neck, and waist (plus hip for women) in centimeters. The tool applies the US Navy log10 formula live and reports your body fat percentage with a fitness category.
Good to know
This Body Fat Calculator estimates your body fat percentage from simple tape-measure readings using the US Navy circumference method. You pick male or female, enter your height, neck, and waist (women also add hip) in centimeters, and it instantly applies the Navy log10 regression to produce a percentage plus a fitness category. It is built for anyone tracking fitness or recomposition who wants a body fat figure without buying calipers, a smart scale, or a DEXA scan.
Reach for it when you want a repeatable, no-cost way to monitor change over weeks rather than a single precise number. The calculation runs entirely in your browser, so it is well suited to logging measurements regularly at home. The Navy formula is sex-specific because fat distribution differs: the men's equation works from waist minus neck, while the women's equation uses waist plus hip minus neck, which is why the hip field appears only for the female setting.
To read your result, look at both the percentage and the category badge. This tool uses different thresholds per sex: for men, under 6% is essential fat, 6 to 14% athletes, 14 to 18% fitness, 18 to 25% average, and 25%+ obese; for women the bands are shifted higher (under 14% essential, up to 21% athletes, 25% fitness, 32% average, and above that obese), reflecting normal physiological differences. The categories are reference ranges, not diagnoses.
For trustworthy numbers, keep your tape placement identical every time: waist at the navel, neck just below the larynx, and hip at the widest point, with the tape snug but not compressing the skin. A few practical caveats:
- Circumference estimates can differ from a DEXA or hydrostatic reading by several percent, so treat the value as a trend indicator.
- Very muscular or larger-waisted builds can skew the result, since the formula infers fat purely from girth.
- Measure at a consistent time of day, as bloating and posture shift waist readings.
Frequently asked questions
Why does the women's formula need a hip measurement?
The US Navy method uses different regression coefficients for each sex, and the women's equation adds hip circumference (waist + hip - neck) because fat distribution differs, which improves accuracy versus the men's waist-only formula.
How accurate is this compared to a body scan?
The US Navy circumference method typically lands within about 3-4% of DEXA or hydrostatic weighing for most people, but consistent, correct tape placement matters; use it to track trends rather than as a clinical body fat value.
Is my data uploaded anywhere?
No — this calculator runs entirely in your browser; nothing is uploaded.
Is this a substitute for medical advice?
No. These are educational estimates — consult a qualified health professional for medical decisions.
People also ask
What measurements do I need for the US Navy body fat formula?
Men need height, neck, and waist circumference; women also need hip circumference. All values are entered in centimeters and measured with a flexible tape.
What is a healthy body fat percentage by gender?
General reference ranges put men around 14-18% for fitness and 18-25% as average, while women sit higher at roughly 21-25% for fitness and up to 32% as average, because women carry more essential fat. These are population reference bands, not personal health targets.
Where exactly should I place the tape to measure waist, neck, and hip?
Measure the waist horizontally at the navel, the neck just below the larynx (Adam's apple) angled slightly downward at the front, and the hip at its widest point. Keep the tape level and snug without squeezing the skin.
Why is my body fat percentage different from my smart scale?
Smart scales use bioelectrical impedance, which is affected by hydration and recent meals, while this tool uses body circumferences. The two methods rely on different assumptions, so some difference between them is expected.
Can the US Navy method be inaccurate for muscular people?
Yes. Because it estimates fat from girth alone, a thick waist or neck from muscle can be read as fat, sometimes overestimating body fat for very muscular builds. People with unusual proportions may see larger errors.
Should I measure body fat before or after eating?
Measurements are most consistent when taken at the same time of day under the same conditions, such as in the morning before eating. Food, water, and bloating can temporarily change waist size and shift the result.
How often should I remeasure to track body fat changes?
Measuring every one to two weeks under the same conditions usually shows a clear trend while avoiding noise from daily fluctuations. Looking at the direction over several readings is more meaningful than any single number.
Does the calculator store or upload my measurements?
No. The calculation runs entirely in your browser and the entered measurements are not sent anywhere or saved on a server.
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