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Body fat percentage via US Navy method
The US Navy body fat calculator uses a straightforward formula developed by Hodgdon and Beckett that requires nothing more than a tape measure. Instead of expensive DEXA scans or hydrostatic weighing, you simply measure your waist, neck, and height — plus your hips if you're a woman — and the formula estimates your body fat percentage with reasonable accuracy. It's one of the most practical tools available for tracking body composition at home.
For men, the formula compares the circumference of the abdomen and neck against height. For women, the hip measurement is added to account for typical fat distribution differences between sexes. For example, a 5'10" man with a 34-inch waist and 15-inch neck would land around 18–19% body fat — comfortably in the "fitness" category. A 5'6" woman with a 28-inch waist, 14-inch neck, and 37-inch hips would estimate around 22–23%, which falls in the average range for women.
Getting consistent measurements is the key to reliable results. Measure your neck just below the larynx, keeping the tape slightly angled downward toward the front. For your waist, men should measure at the navel level, while women should measure at the narrowest point of the abdomen. Hip measurements for women should be taken at the widest point across the buttocks.
Always measure directly against skin, not over clothing. Take each measurement twice and average the two readings if they differ. Measuring in the morning before eating or drinking gives you the most consistent baseline. These small habits make a big difference when you're tracking changes over weeks or months.
You can run your numbers for free at simple-calculator.online, which handles the formula automatically so you don't need to worry about the logarithmic math behind the scenes. Just plug in your measurements and get an instant estimate along with your fitness category.
Body fat percentage ranges vary by sex and age, but general fitness benchmarks are widely accepted. For men, essential fat sits around 2–5%, athletic range is 6–13%, fitness is 14–17%, acceptable is 18–24%, and above 25% is considered obese. For women, essential fat is 10–13%, athletic is 14–20%, fitness is 21–24%, acceptable is 25–31%, and above 32% is considered obese.
Rather than chasing a single number, focus on trends over time. A drop of even 2–3 percentage points through consistent training and nutrition can significantly improve metabolic health markers. The Navy method may slightly overestimate fat in very muscular individuals and underestimate in sedentary ones, so treat it as a useful guide rather than a clinical measurement.
Studies suggest the US Navy formula has a margin of error of roughly 3–4 percentage points compared to DEXA scans. It's less precise than lab methods but significantly more convenient and consistent enough for tracking progress over time.
Every 4–6 weeks is a reasonable interval. Measuring too frequently can create noise from water retention and natural fluctuations. Monthly checks give you a clearer picture of real trends.
This calculator is for informational purposes only and does not replace professional medical advice, diagnosis, or treatment. If you have concerns about your weight, body composition, or overall health, consult a qualified healthcare provider.