How to Use This Calculator
Choose your sex and units, then enter your height, weight, neck (just below the Adam’s apple), waist (at the navel) and, for women, hips (at the widest point). Click Calculate to see your estimated body fat, your category, your fat mass, your lean mass and your FFMI (fat-free mass index).
Why Track Body Fat Alongside Peptide Research
Body composition is one of the few objective markers that shows change over a research cycle involving fat-loss or body-recomposition compounds, alongside weight and progress photos, which is why it’s included here rather than as a standalone fitness tool. Measuring the same way each time (same tape tension, same time of day, ideally first thing in the morning) matters more than any single reading, since consistency is what makes a trend meaningful.
Accuracy and Limitations
The Navy method assumes a fairly typical fat distribution pattern; it tends to be less accurate for very lean or very muscular individuals, where DEXA or hydrostatic weighing are more reliable. Treat the result as a consistent tracking number rather than a lab-grade measurement, the trend over weeks matters far more than any single data point.
US Navy Body Fat Formula, Step by Step
The table follows the male example on this page: 180 cm tall, 80 kg, 38 cm neck and 85 cm waist. The calculator keeps unrounded values, so a hand calculation can differ by a tenth of a percent.
| Step | Working | Result |
|---|---|---|
| 1. Convert to inches | 180 / 2.54, 85 / 2.54, 38 / 2.54 | 70.9 in, 33.5 in, 15.0 in |
| 2. Waist minus neck | 33.5 – 15.0 | 18.5 in |
| 3. Take log10 | log10(18.5) and log10(70.9) | 1.267 and 1.851 |
| 4. Apply the formula | 86.010 x 1.267 – 70.041 x 1.851 + 36.76 | About 16% body fat |
| 5. Fat mass | 80 x 16 / 100 | About 12.9 kg |
| 6. Lean mass | 80 – 12.9 | About 67.1 kg |
For women the formula uses waist + hip – neck instead of waist – neck, with its own constants (see the formula above). Measure the same way each time, because small changes in where the tape sits move the result.
Who Should Use This
Researchers and coaches tracking body composition without calipers or a DEXA scan; anyone monitoring changes in body fat over time.
What This Calculator Does
The Body Fat Percentage Calculator estimates body fat with the US Navy circumference method, which needs only a tape measure. Enter height, neck and waist (plus hip for women) in cm or inches; add weight to also get fat mass, lean mass and fat-free mass index (FFMI).
Formula Used
Men: BF% = 86.010 × log₁₀(Waist − Neck) − 70.041 × log₁₀(Height) + 36.76Women: BF% = 163.205 × log₁₀(Waist + Hip − Neck) − 97.684 × log₁₀(Height) − 78.387Fat mass = Weight × BF% ÷ 100; Lean mass = Weight − Fat massFFMI = Lean mass (kg) ÷ Height (m)²Example Calculation
Limitations
The Navy method typically lands within about 3 to 4 percentage points of DEXA and is less accurate at very low or very high body fat. Small tape-measurement errors noticeably change the result, so measure the same way each time.
Frequently Asked Questions
How does the US Navy body fat formula work?
The US Navy method estimates body fat percentage using circumference measurements (neck, waist, and hips for women) alongside height. It applies a logarithmic formula validated against hydrostatic weighing data, making it more accurate than BMI for muscular individuals while requiring only a flexible measuring tape.
How accurate is the US Navy body fat calculator?
The Navy formula has a margin of error of approximately ±3-4% body fat compared to gold-standard DEXA scanning. Accuracy improves with careful, consistent measurements. It is more reliable than BMI but less precise than DEXA, BodPod, or hydrostatic weighing for individuals with atypical body composition.
Where exactly should I measure my waist and neck for accurate results?
Neck: measure at the narrowest point, just below the larynx (Adam's apple), with the tape perpendicular to the long axis of the neck. Waist: measure at the navel for men; at the narrowest point of the abdomen for women. Take measurements after a normal exhale and ensure the tape is level and snug but not compressing skin.
What are healthy body fat percentage ranges for men and women?
For men: essential fat 2-5%, athletes 6-13%, fitness 14-17%, acceptable 18-24%, obese 25% and above. For women: essential fat 10-13%, athletes 14-20%, fitness 21-24%, acceptable 25-31%, obese 32% and above. These ranges are general guidelines; optimal levels vary by age and individual health status.
How do I calculate body fat with the US Navy formula?
Convert your height, neck and waist to inches (cm divided by 2.54). For men, subtract the neck from the waist, take log10 of that and of your height, then work out 86.010 x log10(waist - neck) - 70.041 x log10(height) + 36.76. For women, use waist + hip - neck in place of waist - neck, with the constants 163.205, 97.684 and 78.387 as shown in the formula section. The calculator does these steps for you.
How do I work out fat mass and lean mass from my body fat percentage?
Fat mass is your weight multiplied by body fat percent and divided by 100. Lean mass is your weight minus the fat mass. For example, at 80 kg and about 16% body fat, fat mass is 80 x 16 / 100, about 12.9 kg, and lean mass is about 67.1 kg. The calculator shows both numbers, plus FFMI, once you enter your weight.