§ · Body Fat (US Navy)
US Navy bodyfat calculator.
Three to four circumference measurements. Two minutes with a tape measure. A reasonable body-fat estimate without DEXA.
§ · Calculator
US Navy circumference method86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
§ 01 · How to measure
Neck: just below the larynx, parallel to the floor. Stand relaxed.
Waist:men measure at the navel; women measure at the narrowest point. Don't suck in.
Hip (women): the widest point of the hips, parallel to the floor.
Use a soft tape measure (cloth or vinyl). Pull snug but don't compress the tissue. Take each measurement three times and use the median if they disagree by more than a centimetre.
§ 02 · The formula
Men: 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
Women: 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
All measurements in centimetres. The calculator handles unit conversion when you pick inches.
This is an estimate, not DEXA. Expect to be within ±3% of the actual number for most body types. The estimate gets less reliable at the extremes (very lean, very obese).
§ 03 · Body-fat percentage categories
Once you have a number, here is roughly where it sits. These are the American Council on Exercise (ACE) general categories — useful as a frame, not a verdict. Healthy ranges differ by age, sport, and genetics.
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Acceptable | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
“Essential fat” is the minimum the body needs for normal function — dropping below it is not a goal. Most people targeting “lean and healthy” aim for the fitness band.
§ 04 · How BiteDeck uses this
In the app, saved BF% entries feed two places: the Home Composition page (the visible chart) and the Katch–McArdle BMR used by the weight forecast. You only have to enter it once — the app remembers and uses it daily.
§ 05 · Other methods we support
BiteDeck supports four BF estimation paths in the app:
- US Navy (this calculator).
- Deurenberg (BMI + age + sex).
- Manual entry (DEXA, calipers, scale, whatever).
- HealthKit import (from a connected scale or another app).
Now that you have a number, plug it into the Katch–McArdle BMR calculator for a body-fat-aware metabolic rate.
§ 06 · FAQ
How accurate is the US Navy body fat calculator?
For most body types it lands within about ±3% of a DEXA or hydrostatic reading — close enough to track change over time. It gets less reliable at the extremes (very lean or very high body fat), and a sloppy tape measurement is the biggest source of error. Measure each circumference three times and use the median.
What measurements do I need?
Height, neck, and waist for men; height, neck, waist, and hip for women. A soft cloth or vinyl tape measure is all the equipment required — no calipers, no scale, no lab.
What is a healthy body fat percentage?
It depends on sex. For men, roughly 14–24% is the fitness-to-acceptable range; for women, roughly 21–31%. Athletes sit lower (men 6–13%, women 14–20%). See the category table above for the full breakdown by sex.
Is the Navy method better than BMI?
For body composition, yes. BMI is just weight over height squared — it cannot tell muscle from fat, so a lean, muscular person reads as "overweight." The Navy method estimates actual fat mass from circumferences, which is what you usually care about.
Where exactly do I measure my waist?
Men measure at the navel; women measure at the narrowest point of the torso. Keep the tape parallel to the floor, pull it snug without compressing the skin, and breathe out normally — do not suck in.