Body Fat Calculator (Navy Method)

Body Fat Percentage: What It Means and How to Measure It

Body fat percentage is the proportion of your total body weight that is composed of fat tissue. Unlike BMI, which only accounts for height and weight, body fat percentage distinguishes between fat mass and lean mass (muscle, bone, water, and organs). This makes it a more accurate indicator of health and fitness than weight or BMI alone. Two people can weigh the same but have very different body compositions and health outcomes.

The U.S. Navy Method

The U.S. Navy body fat formula, also known as the Navy circumference method, was developed by Hodgdon and Beckett at the Naval Health Research Center. It estimates body fat percentage from simple tape measurements: height, neck circumference, and waist circumference for men, with the addition of hip circumference for women. The formula uses logarithmic equations calibrated against hydrostatic (underwater) weighing data to produce an estimate that is typically accurate to within 3–4 percentage points of methods like DEXA scanning.

For men, the formula is: 495 / (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450. For women, the formula is: 495 / (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450. All measurements must be in centimeters for the formula to produce correct results.

Healthy Body Fat Ranges

Healthy body fat ranges differ significantly between men and women due to biological differences in fat storage. Women naturally carry more essential fat for reproductive and hormonal functions. For men, essential fat is roughly 2–5%, with athletic levels at 6–13%, fitness levels at 14–17%, average at 18–24%, and obese above 25%. For women, essential fat is 10–13%, athletic levels are 14–20%, fitness is 21–24%, average is 25–31%, and obese is above 32%.

Extremely low body fat percentages can be as dangerous as extremely high ones. Essential fat is required for normal physiological function, including hormone production, temperature regulation, and organ protection. Athletes who maintain very low body fat levels should do so under medical supervision.

Other Body Fat Measurement Methods

• DEXA Scan: Dual-energy X-ray absorptiometry is considered the gold standard for body composition analysis. It provides regional fat distribution data and is accurate to within 1–2%, but requires clinical equipment and typically costs $50–150 per scan.
• Hydrostatic Weighing: Underwater weighing measures body density by comparing weight on land to weight submerged in water. It is accurate to within 2–3% but requires specialized equipment and full submersion.
• Bioelectrical Impedance (BIA): Smart scales and handheld devices send a small electrical current through the body. Accuracy varies widely (3–8% margin of error) based on hydration levels, meal timing, and device quality.
• Skinfold Calipers: A trained technician measures skin folds at 3–7 body sites. Accuracy depends heavily on the skill of the person taking measurements, with a typical error range of 3–5%.
• Bod Pod (Air Displacement): Measures body volume using air displacement in a sealed chamber. Accuracy is similar to hydrostatic weighing at 2–3%, and it does not require water submersion.

Accuracy and Limitations of the Navy Method

The Navy method is popular because it requires only a flexible tape measure and takes less than a minute. However, it has limitations. Individuals with unusual body proportions, such as very muscular necks or narrow waists relative to their overall size, may see skewed results. The formula was originally calibrated on U.S. military personnel and may be less accurate for different populations. For tracking changes over time, consistency in measurement technique is more important than absolute accuracy — always measure at the same time of day, at the same anatomical landmarks, and with the same tape tension.