- Navy method, 1984
- Inches or cm
- 5 ACE bands
- ±3–4% vs DEXA
A body fat calculator that shows you where the tape goes
Neck, waist, and height go in. You get your US Navy body-fat percent on an ACE category gauge, the fat and lean mass behind it, a placement note on every field so the tape sits where the formula expects, and the real ±3–4% spread against a DEXA scan.
Start measuringStand tall with no shoes, heels together and looking straight ahead. Round down to the nearest half-inch.
Measure just below the larynx (your Adam's apple), letting the tape slope slightly down toward the front. Keep it snug, not tight. Round up to the nearest half-inch.
Wrap the tape around your bare waist at the navel. Exhale normally and don't suck in. Round down to the nearest half-inch.
Optional. Add your weight to see fat mass and lean mass in pounds.
Enter your height, neck, and waist measurements to see your US Navy body-fat percentage update live.
Navy body-fat reference: category bands, tape placement, valid ranges, check readings
Most of the doubt around a tape estimate lives in a handful of small decisions: which landmark the tape actually sits on, which way to round a half inch, whether a given waist even produces a valid number, and which category band a percentage falls into. This reference gathers the lookup values behind those decisions, the two sets of formula coefficients, the input ranges the calculator accepts, and a table of pre-computed readings you can measure yourself against.
Body-fat category bands (ACE, by sex)
The percentage is mapped onto the American Council on Exercise ranges, and the cutoffs differ by sex, so the same number sorts into a different band for a man and a woman.
| Band | Men (BF%) | Women (BF%) |
|---|---|---|
| Essential | 2–5% | 10–13% |
| Athletic | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| High | 25% and up | 32% and up |
Women's floors run higher across every band because more of their essential fat is structural. A single shared color bar would mislabel one sex, which is why the gauge on the tool switches thresholds with the sex you set.
Where the tape sits and which way to round
Placement and rounding drive most of the error in a tape reading. Round each figure to the nearest half unit before you type it; a tenth of an inch is precision the equation cannot use.
| Measurement | Where to place the tape | Rounding | Common error |
|---|---|---|---|
| Neck | Just below the larynx, angled slightly down at the front | Up, to nearest 0.5 in / 0.5 cm | Riding over the Adam's apple, which inflates it |
| Waist (men) | Across the navel, relaxed, after a normal exhale | Down | Sucking in, or measuring at the narrowest point |
| Waist (women) | At the navel, relaxed, normal breath | Down | Pulling the tape tight instead of snug |
| Hip (women) | Around the widest part of the buttocks | Down | Measuring at the hip bone rather than the widest point |
| Height | Standing straight, no shoes, heels together | Down | Rounding up to a flattering figure |
The asymmetry is deliberate. Rounding the neck up while rounding the waist down nudges the estimate slightly high rather than flattering it, so a drop across a few weeks reads as a real change and not as rounding noise.
Input ranges, unit conversions, and invalid readings
Decimal and half-inch entries are accepted and used as typed, never truncated. A reading is only shown once inputs are complete and the result lands in a plausible domain; otherwise the tool holds at a guidance state instead of printing a stale, zero, or negative number.
| Condition | What the tool does |
|---|---|
| Waist minus neck at or below zero (men) | No result; the log term is undefined, so re-check the tape |
| Waist plus hip minus neck at or below zero (women) | No result; same undefined log term |
| Computed BF% below 0 or above 60 | Flagged invalid rather than displayed |
| Bodyweight left blank | BF% and band still render; a prompt replaces the fat/lean mass figures |
| Half-inch value such as 34.5 | Accepted and fed to the formula unchanged |
Quick conversions for switching between imperial and metric measurements:
| Convert | Multiply by |
|---|---|
| Inches to centimetres | 2.54 |
| Centimetres to inches | 0.3937 |
| Feet to centimetres | 30.48 |
| Pounds to kilograms | 0.4536 |
| Kilograms to pounds | 2.2046 |
Reference readings to check your result against
The two regressions carry separate coefficients, listed here so a hand calculation lines up with the tool. All circumferences are in inches.
| Coefficient applies to | Men | Women |
|---|---|---|
| log10(waist − neck) / log10(waist + hip − neck) | 86.010 | 163.205 |
| log10(height) | −70.041 | −97.684 |
| Fixed constant | +36.76 | −78.387 |
Worked measurement sets across the band range, rounded to a tenth of a percent:
| Sex | Height | Neck | Waist | Hip | BF% | Band |
|---|---|---|---|---|---|---|
| Male | 70 in | 16 in | 31 in | N/A | 8.7% | Athletic |
| Male | 71 in | 15 in | 32.5 in | N/A | 14.0% | Fitness |
| Male | 69 in | 16 in | 36 in | N/A | 19.9% | Average |
| Male | 68 in | 16.5 in | 40 in | N/A | 26.3% | High |
| Female | 64 in | 13 in | 26 in | 35 in | 19.6% | Athletic |
| Female | 65 in | 13 in | 27 in | 36 in | 21.8% | Fitness |
| Female | 64 in | 12.5 in | 28 in | 37 in | 25.9% | Average |
| Female | 67 in | 13.5 in | 32 in | 41 in | 32.8% | High |
If your own numbers land within a percent of the matching row, your measurement technique is sound. A larger gap usually points at the tape placement rather than the arithmetic.
Related concepts
- TDEE and maintenance calories: the daily energy figure a body-fat number helps you plan a cut around.
- Macronutrient split: dividing that calorie target into protein, carbs, and fat once you know your lean mass.
- Lean body mass: total weight minus fat mass, and the base most protein targets are set from.
- DEXA and hydrostatic weighing: the lab references the tape method was trained to reproduce and is measured against.
- BMI: the height-and-weight-only screen the circumference method is meant to improve on for lean and heavier-necked builds.