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.
*12 month plan, billed once for the term when a physician approves. Renews each term.
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.
Start here · one question
What's your goal weight?
Choose a goal to discuss with your clinician. You can change it in your intake.
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.
