How accurate is the Navy method?

Typically ±3.5% vs DXA gold standard for adults in the 10–30% body-fat range. Accuracy degrades at the extremes — very lean people (sub-10% men, sub-15% women) and very obese people are systematically estimated slightly off.

Where do I measure my waist?

Men: the narrowest point above the navel (often slightly above the belly button — find the smallest circumference). Women: at the level of the navel. Both measurements are taken standing relaxed, not sucked in.

Where is my neck measurement?

Just below the larynx ('Adam's apple'), perpendicular to the long axis of the neck. The tape should sit flat all the way around without being pulled tight.

Why a different formula for women?

Women carry a higher essential-fat percentage (10–13% vs 2–5% for men) and distribute fat differently — the hip measurement captures that distribution. The Hodgdon-Beckett women's formula was calibrated separately on a female cohort.

What's 'essential fat'?

The amount of body fat required for basic physiological function — protecting organs, hormone production, vitamin storage. Going below the essential threshold (2–5% for men, 10–13% for women) causes hormonal disruption, especially in women (amenorrhea, bone-density loss).

How does this compare to BMI?

BMI doesn't distinguish fat from muscle and overestimates risk for athletes. Body-fat percentage is the more meaningful number when assessing fitness or health composition. Use them together: BMI for population-level screening, body-fat for personal context.

Is the calculator's number stored anywhere?

No. Like every Convertitive tool, this one runs entirely in your browser. Measurements are not sent to a server, logged, or persisted between sessions.

Body Fat Percentage Calculator — US Navy Method

Three tape measurements, one body-fat percentage — the most accurate field method.

The US Navy body-fat method is the gold-standard tape-only estimator. It was developed by the Navy Health Research Center in 1984 (Hodgdon & Beckett) to replace skinfold calipers, and repeated validation studies have placed its accuracy within ±3.5% of dual-energy X-ray absorptiometry (DXA). Convertitive runs the original equations exactly; the only inputs are circumferences you can measure at home with a fabric tape.

Height (cm)

Waist (cm)

Neck (cm)

Waist: narrowest point above the navel

Body fat — US Navy method

23.0%

Average

Men's body-fat ranges

Essential fat2–5%
Athletes6–13%
Fitness14–17%
Average18–24%
Obese25–+%

US Navy method (Hodgdon-Beckett 1984). Typical accuracy ±3.5% vs DXA-scan gold standard for the general adult population — less accurate for trained athletes with low fat and very lean physiques. Measure with a tape, not a tailor’s caliper.

How to use

Pick your sex
The formulas have separate constants because of typical fat-distribution differences. The form changes to ask for hip measurement when 'Female' is selected.
Measure with a fabric tape
Stand relaxed. Waist (men): narrowest point above the navel. Waist (women): at the level of the navel. Neck: below the larynx, perpendicular to the long axis. Hip (women): widest point of the buttocks, parallel to the floor.
Read the percentage and category
The number is your estimated body fat. The category badge shows where you sit in the standard ACE body-composition bands.

Reference ranges (American Council on Exercise)

Category	Men	Women
Essential fat	2–5%	10–13%
Athletes	6–13%	14–20%
Fitness	14–17%	21–24%
Average	18–24%	25–31%
Obese	25%+	32%+

Frequently asked questions

How accurate is the Navy method?: Typically ±3.5% vs DXA gold standard for adults in the 10–30% body-fat range. Accuracy degrades at the extremes — very lean people (sub-10% men, sub-15% women) and very obese people are systematically estimated slightly off.
Where do I measure my waist?: Men: the narrowest point above the navel (often slightly above the belly button — find the smallest circumference). Women: at the level of the navel. Both measurements are taken standing relaxed, not sucked in.
Where is my neck measurement?: Just below the larynx ('Adam's apple'), perpendicular to the long axis of the neck. The tape should sit flat all the way around without being pulled tight.
Why a different formula for women?: Women carry a higher essential-fat percentage (10–13% vs 2–5% for men) and distribute fat differently — the hip measurement captures that distribution. The Hodgdon-Beckett women's formula was calibrated separately on a female cohort.
What's 'essential fat'?: The amount of body fat required for basic physiological function — protecting organs, hormone production, vitamin storage. Going below the essential threshold (2–5% for men, 10–13% for women) causes hormonal disruption, especially in women (amenorrhea, bone-density loss).
How does this compare to BMI?: BMI doesn't distinguish fat from muscle and overestimates risk for athletes. Body-fat percentage is the more meaningful number when assessing fitness or health composition. Use them together: BMI for population-level screening, body-fat for personal context.
Is the calculator's number stored anywhere?: No. Like every Convertitive tool, this one runs entirely in your browser. Measurements are not sent to a server, logged, or persisted between sessions.

About

The Hodgdon-Beckett equations

Men: %BF = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. Women: %BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. All circumferences in cm. The Navy adopted this in 1984 to replace inconsistent caliper measurements; nearly every modern body-fat 'tape test' is some refinement of it.

When to use DXA or BodPod instead

If body composition is medically relevant (athlete performance contracts, treatment for eating disorders, cancer recovery), get a DXA scan or BodPod measurement. The tape method is good enough for personal goal-setting; it isn't a substitute for clinical-grade measurement when stakes are high.