How accurate is the US Navy body fat formula?

Roughly plus or minus 3 to 4% versus DEXA for the general adult population. Validation studies (Knechtle 2011, Hodgdon 1984) found the formula correctly classifies body composition for most people but can over- or under-estimate by 5% or more at the extremes of leanness and obesity. For a precision number, DEXA or hydrostatic weighing are the gold standards.

Why does the women's formula use hip and the men's does not?

Women carry more body fat in the gynoid region (hips and thighs), and the formula needs to account for that distribution. The men's formula is well-predicted by neck and waist alone because male fat tends to accumulate centrally (visceral and android). The two formulas use the same underlying regression approach but with different anatomical predictors.

What is the difference between essential fat and total body fat?

Essential fat is the minimum body fat required for physiological function: cell membranes, nervous system insulation, hormone production, bone marrow. It is roughly 2 to 5% for men and 10 to 13% for women (women have higher essential fat to support reproductive function). Total body fat is everything stored beyond essential fat, including subcutaneous and visceral depots.

Is low body fat always healthier?

No. Below essential fat thresholds, hormonal disruption, immune compromise, reduced bone density, and (in women) menstrual dysfunction become common. The healthy range is broader than fitness culture suggests. Most clinically healthy adults sit between 12 to 20% (men) and 20 to 30% (women), depending on age and activity. The athletic band is a fitness target, not a health requirement.

What is your body fat percentage?

Jillian Foglesong Stabile, MD

FAAFP, DABOM · Reviewed June 10, 2026 · US Navy method

Sex assigned at birth (the equation uses this)

Height (feet)

Height (inches)

Neck

Waist

Hip

Women only; leave blank for men.

Estimate only, not a diagnosis. The US Navy method is a directional screen, not a substitute for clinical body composition testing, and a licensed physician determines what is healthy for you. Individual results vary.

Chapter 01 · The method

How the US Navy formula works

The result above comes from a regression formula developed by Hodgdon and Beckett at the Naval Health Research Center in 1984, built so the military could screen body composition with nothing more than a tape measure.¹ For men, the inputs are height, neck, and waist. For women, the formula adds the hip circumference, because women carry more fat in the gynoid region of the hips and thighs and a neck-and-waist-only model would systematically under-read it.

Both versions use the same logarithmic regression approach; they differ only in which circumferences feed the equation. The output is an estimate of total body fat as a percentage of body mass, which is the figure clinicians and trainers care about far more than the single number on a bathroom scale.

Band	Range	What it represents
Essential fat (women)	10 to 13%	The physiological minimum for women
Healthy range (women)	20 to 30%	The broad healthy band for women
Essential fat (men)	2 to 5%	The physiological minimum for men
Healthy range (men)	12 to 20%	The broad healthy band for men

Indicative body composition bands. Healthy ranges widen with age.

Chapter 02 · The technique

How to measure correctly

Accuracy lives in the tape. Use a flexible, non-stretch tape and stand relaxed, breathing normally. Measure the neck just below the larynx, the waist at the navel for men or at the narrowest point for women, and the hip at its widest point for women. Measure each site twice and average the readings; a sucked-in waist is the most common source of a falsely low number.

The point: same tape, same posture, same time of day. Consistency in how you measure matters more than the absolute number on any single attempt. Individual results vary.

Chapter 03 · The fine print

Where the estimate misses

The formula was developed on a general adult population, so very lean and very obese individuals sit outside its validation range and can be off by 5% or more. Bodybuilders and people with unusual fat distribution may score artificially low. For a precision figure, DEXA and hydrostatic weighing remain the gold standards. Treat this result as a directional screen, not a clinical measurement. A physician determines what is healthy for you. Individual results vary.

Every medication on sipra is prescribed by a licensed physician, so your care always starts with a visit. Your sipra membership gives you ongoing access to those physician visits, so you can check in, adjust your plan, and ask questions whenever you need, without paying per visit. It is how we keep high-quality care convenient: one membership, physician access whenever you need it, and support at every step.

Sources

Hodgdon JA, Beckett MB. "Prediction of percent body fat for US Navy men and women from body circumferences and height." NHRC Reports 84-11, 84-29. 1984. dtic.mil
Knechtle B et al. "Comparison of anthropometric methods to estimate body fat." 2011. pubmed.ncbi.nlm.nih.gov
American Council on Exercise. "Percent Body Fat Norms." ACE body composition standards. acefitness.org

Compounded medications are not FDA-approved and require a patient-specific prescription. Brand names are trademarks of their owners; sipra is not affiliated with them.

General education, not medical advice. Last reviewed June 10, 2026 by Jillian Foglesong Stabile, MD, FAAFP, DABOM. Prices snapshot US Navy method. Individual results vary.