Body Fat Percentage Calculator
Estimate your body fat percentage using the US Navy circumference method. Enter your height, waist, and neck measurements to get a clinically-validated fat percentage result.
About this calculator
The US Navy body fat method estimates fat percentage from simple body circumference measurements rather than requiring expensive equipment. For males, the formula is: BF% = 495 / (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450. For females, hip measurement is added: BF% = 495 / (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450. These equations were derived by the US Navy to classify recruits by body composition without underwater weighing. The logarithmic terms reflect how circumference differences scale with actual fat tissue volume. Results within 3–4 percentage points of DEXA scans make this one of the most practical field methods available.
How to use
Suppose a male is 180 cm tall, has a 90 cm waist, and a 38 cm neck. Step 1: Compute waist − neck = 90 − 38 = 52 cm. Step 2: log10(52) ≈ 1.7160; log10(180) ≈ 2.2553. Step 3: Denominator = 1.0324 − 0.19077 × 1.7160 + 0.15456 × 2.2553 = 1.0324 − 0.3274 + 0.3486 = 1.0536. Step 4: BF% = 495 / 1.0536 − 450 ≈ 469.8 − 450 = 19.8%. This man's estimated body fat is approximately 19.8%, which falls in the fitness category.
Frequently asked questions
How accurate is the US Navy body fat percentage method compared to DEXA?
The US Navy method typically falls within 3–4 percentage points of DEXA (dual-energy X-ray absorptiometry), which is considered the gold standard. Accuracy depends heavily on taking measurements correctly — always measure waist at the navel and neck just below the larynx. It tends to be slightly less accurate for very lean or very obese individuals where circumference ratios deviate from the population used to build the formula. For most healthy adults it provides a reliable and free alternative to lab testing.
What is a healthy body fat percentage for men and women?
For men, essential fat is around 2–5%, athletes typically range 6–13%, fitness levels are 14–17%, acceptable is 18–24%, and above 25% is considered obese. For women, essential fat is 10–13%, athletes 14–20%, fitness 21–24%, acceptable 25–31%, and above 32% is considered obese. These ranges are defined by the American Council on Exercise. Age also plays a role — body fat naturally increases with age even when weight stays constant, so context matters when interpreting results.
Why does the Navy body fat formula use logarithms instead of direct measurements?
Circumference measurements don't scale linearly with fat volume because the body is roughly cylindrical — doubling a circumference more than doubles the cross-sectional area. Logarithmic transformation compresses this non-linearity and produces a formula that performs consistently across a wide range of body sizes. The original Navy researchers found that log-transformed circumference differences correlated strongly with hydrostatic (underwater) weighing results, which was the validation dataset. Using raw centimeters without the log transformation would produce much larger errors at the extremes of the body size distribution.