How the US Navy body fat method works
The US Navy circumference method estimates body fat from two or three simple tape-measure readings rather than calipers or a body-composition scale. For men, you measure your neck and waist; for women, add your hip. The measurements feed into a logarithmic formula published by the US Department of Defense, which has been validated against underwater weighing in large military cohorts.
The formula (all measurements in centimetres): Men: Body fat % = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450 Women: Body fat % = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450
How to measure correctly
- Neck: measure just below the larynx (Adam's apple), tilting the tape slightly downward at the front. Keep the tape snug but not tight.
- Waist (men): measure at the navel. Keep the tape horizontal and parallel to the floor.
- Waist (women): measure at the narrowest point of the torso, usually just above the navel.
- Hip (women only): measure around the widest part of the hips and buttocks, keeping the tape horizontal.
- Take each measurement twice and average if the readings differ by more than 0.5 cm.
- Measure in the morning before eating, wearing minimal clothing.
Body fat categories
The American Council on Exercise (ACE) defines these categories for adult body fat percentage:
- Essential fat — Men ≤ 5 % / Women ≤ 13 % (minimum required for organ function)
- Athlete — Men 6–13 % / Women 14–20 %
- Fitness — Men 14–17 % / Women 21–24 %
- Average — Men 18–24 % / Women 25–31 %
- Above average — Men ≥ 25 % / Women ≥ 32 %
How accurate is this method?
The Navy method is a screening tool, not a clinical measurement. Studies show a typical error of ±3–4 percentage points compared with DEXA scans. Accuracy drops if measurements are taken inconsistently, and the formula was derived primarily from military-age adults, so it may be less precise for older adults or very muscular individuals. Use it to track trends over time rather than as an absolute number.
For a more complete picture, pair this result with your BMI and your TDEE. Entering your body fat % in the shared profile lets the TDEE calculator switch to Katch-McArdle, which produces a more accurate basal metabolic rate for muscular or lean individuals. Swoodie tracks your nutrition day-to-day, making it easier to act on what these numbers are telling you.
This calculator provides a general estimate for healthy adults and is not medical advice. Body composition results vary with measurement technique and individual physiology. Consult a doctor or registered dietitian before making significant changes to your diet or exercise routine.
Frequently asked questions
What is body fat percentage?
Body fat percentage is the proportion of your total body weight that is fat tissue. The remainder is lean mass — muscle, bone, organs, and water. A healthy body fat range varies by sex: most guidelines put 14–24 % as the fitness-to-average range for men and 21–31 % for women, though athletes often sit well below those figures.
How accurate is the US Navy body fat formula?
Studies show the Navy circumference method has a typical error of ±3–4 percentage points versus DEXA scanning. Accuracy depends heavily on consistent tape placement. It is most useful for tracking directional changes over weeks or months rather than as a precise one-time measurement.
Why does this calculator need neck, waist, and hip measurements?
The Navy formula uses the difference between waist (where most abdominal fat sits) and neck (a leaner circumference) as a proxy for fat mass. For women, hip circumference is added because female fat distribution includes the hip and gluteal region. The logarithm of height adjusts for stature. No single tape measurement could capture this — the combination is what makes the formula work.
What should I do with my body fat result?
Use it as a baseline and a trend indicator. If your body fat is higher than your target, the most effective lever is your daily energy balance — use the TDEE calculator to find your maintenance calories, then create a moderate deficit. Preserving lean mass while losing fat requires adequate protein intake; the protein calculator can help you set a target.
Can I use this calculator if I am very muscular or very lean?
The formula was calibrated on a general military population, so it can underestimate body fat in very lean, well-muscled individuals and overestimate it in those with an unusual fat distribution. If you have a large neck circumference due to muscle rather than fat, the result will skew low. DEXA scanning or hydrostatic weighing gives a more accurate measurement in those cases.