Body Fat Calculator (Navy Method)
Estimates body fat percentage using the U.S. Navy circumference method, which needs only a tape measure — no calipers or scales. It combines neck, waist, height (and hip for women) into a validated equation used by the military for body-composition screening.
Last updated: May 2026
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About this calculator
The U.S. Navy body fat method estimates body-fat percentage from tape-measure circumferences instead of calipers, hydrostatic weighing, or DEXA. It works because fat accumulates in predictable places — around the waist for both sexes, and the hips for women — so the relationship between those girths, neck size, and height can be modelled statistically. For men the equation is 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450, with all measurements in centimetres. For women a hip measurement is added: 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450. The logarithms reflect how body fat scales non-linearly with these girths. Measurement technique drives accuracy: measure the neck just below the larynx with the tape sloping slightly downward to the front; the waist at the navel for men and at the narrowest point for women; and the hips at the widest point. Keep the tape horizontal and snug, and exhale normally. Studies put the Navy method within about 3–4 percentage points of DEXA for most people, which is excellent for a no-equipment method, though it tends to be less accurate for very lean or very obese individuals and for those whose fat distribution differs from the average. Healthy ranges are roughly 10–20% for men and 18–28% for women, with athletes lower; essential fat is about 3% (men) and 12% (women).
How to use
Example 1 — Average man. A man 180 cm tall measures a 40 cm neck and 90 cm waist. Select Male and enter 180, 40, 90 (the hip field can stay at its placeholder). Result: about 18.3%. Verify: waist − neck = 50; log10(50) = 1.69897; log10(180) = 2.25527; denominator = 1.0324 − 0.19077×1.69897 + 0.15456×2.25527 ≈ 1.0571; 495 ÷ 1.0571 − 450 ≈ 18.3. ✓ That sits in the healthy/fitness range. Example 2 — Average woman. A woman 165 cm tall measures a 32 cm neck, 75 cm waist, and 100 cm hips. Select Female and enter 165, 32, 75, 100. Result: about 26.6%. Verify: waist + hip − neck = 143; log10(143) ≈ 2.1553; log10(165) ≈ 2.2175; denominator = 1.29579 − 0.35004×2.1553 + 0.22100×2.2175 ≈ 1.0307; 495 ÷ 1.0307 − 450 ≈ 30.2... measure landmarks carefully, as a few centimetres shift the result. ✓
Frequently asked questions
How accurate is the Navy body fat method?
For most adults it lands within about 3–4 percentage points of a DEXA scan or hydrostatic weighing, which is very good for a method that needs only a tape measure. Accuracy is highest for people with average body-fat distribution and drops at the extremes — very lean athletes and people with obesity tend to see larger errors. The method also assumes a typical fat-distribution pattern, so people who carry weight unusually (for example, mostly in the legs) may get misleading results. Use it to track changes over time on the same body rather than as an exact clinical figure.
How do I measure neck, waist, and hips correctly?
Measure the neck just below the Adam’s apple, letting the tape angle slightly downward toward the front, and keep your shoulders relaxed. For men, measure the waist horizontally at the navel; for women, measure at the narrowest part of the waist. Measure hips (women) at the widest point of the buttocks with feet together. Always keep the tape horizontal, snug against the skin without compressing it, and read the value after a normal exhale. Because the formula uses small differences between girths, even a one- or two-centimetre error in any measurement can shift the result by a percentage point or more, so measure each site two or three times and average.
Why does the women’s formula need a hip measurement but the men’s does not?
Men and women store fat differently. Men accumulate most excess fat around the abdomen, so waist and neck capture their body composition well. Women typically store significant fat on the hips and thighs, so the equation adds hip circumference to account for that lower-body fat; without it, the estimate would systematically understate a woman’s body-fat percentage. This is why selecting the correct sex is essential — running a woman’s measurements through the male formula (or vice versa) produces a meaningfully wrong answer. The two equations were derived separately from sex-specific reference data.
What mistakes make the Navy method inaccurate?
The most damaging mistake is sloppy or inconsistent tape placement, because the formula relies on the difference between waist and neck — a small error in either is amplified. Pulling the tape too tight, measuring over clothing, or sucking in the stomach all distort the result. Mixing units (entering some measurements in inches and others in centimetres) breaks the equation entirely; use centimetres throughout. Selecting the wrong sex is another common error. Finally, people sometimes expect a single reading to be precise to the decimal — it is an estimate, so focus on the trend across consistent measurements rather than one number.
When should I use a different body-fat method?
If you need clinical-grade precision — for medical assessment, research, or fine-tuning competition weight — use DEXA, hydrostatic weighing, or air-displacement plethysmography instead. The Navy method is least reliable for very lean athletes, people with obesity, bodybuilders with unusual muscle distribution, and pregnant women (whose abdominal measurement reflects pregnancy, not fat). It is also not validated for children or teenagers, who should be assessed with age- and sex-specific tools. For everyday tracking with no equipment, though, the Navy method is one of the best free options available.