On this page (11)
How to use this calculator#
- Measure the neck just below the larynxStand tall, look straight ahead, and run the tape around the neck immediately below the Adam's apple, sloping very slightly downward at the front. Do not flex or tuck the chin — both shrink the reading. Neck girth is subtracted in the formula, so a neck measured 1 cm too large lowers the body fat estimate by roughly a percentage point.
- Measure the waist at the right landmark for your sexMen: horizontally at navel level. Women: at the narrowest part of the torso, usually midway between the lowest rib and the top of the hip bone. Keep the tape level all the way round — check the back in a mirror, because a tape that rides up behind you reads short.
- Take the reading at the end of a normal breath outBreathe in, breathe out normally, and read the tape at the end of that relaxed exhale without sucking in. Holding a breath or bracing the abdomen can change waist girth by 3–4 cm, which is 3–4 percentage points of body fat — larger than the entire difference between the fitness and average bands.
- Women: add the hip measurement at the widest pointAround the fullest part of the buttocks with feet together, tape level and parallel to the floor. The female equation needs it because fat distributed around the hips and thighs is invisible to a waist measurement alone.
- Average three readings, taken the same way each timeMeasure first thing in the morning, unclothed or in thin underwear, tape snug but not compressing the skin. Take each site three times and average. When you re-measure in a few weeks, repeat the identical protocol — the trend is reliable even when the absolute number is not.
The formula#
US Navy circumference method (Hodgdon & Beckett, Naval Health Research Center, 1984)
Men: %BF = 495 ÷ [1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)] − 450 • Women: %BF = 495 ÷ [1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.221 × log₁₀(height)] − 450
- %BF
- Estimated body fat as a percentage of total body mass
- waist
- Waist circumference in centimetres — at the navel for men, at the narrowest point for women
- neck
- Neck circumference in centimetres, taken just below the larynx
- hip
- Hip circumference in centimetres at the widest point — female equation only
- height
- Standing height in centimetres
- log₁₀
- Base-10 logarithm
Developed on US Navy personnel — an adult military population, generally younger and leaner than the public — and validated against hydrostatic weighing. That derivation is why it drifts at the extremes: it tends to overestimate on very lean, heavily muscled bodies and can misread people whose fat sits mostly outside the measured sites. The alternative shown in the tool is the Deurenberg BMI-based estimate: %BF = 1.2 × BMI + 0.23 × age − 10.8 × sex − 5.4, where sex is 1 for men and 0 for women.
How the US Navy tape method works#
The Navy circumference method predicts body fat from the ratio between girth measurements and height. For men it uses waist minus neck; for women it uses waist plus hip minus neck. Both are fed through a logarithmic regression developed by the Naval Health Research Center, which is why a small tape error at the waist moves the result more than you would expect.
Measure first thing in the morning, unclothed, with the tape snug but not compressing skin. Take the neck just below the larynx, the waist at the navel for men and at the narrowest point for women, and the hips at the widest point. Average three readings; a one centimetre difference at the waist typically shifts the estimate by about one percentage point.
Reading the result and the BMI fallback#
Typical bands for men are 6-13% athletic, 14-17% fitness, 18-24% average and 25% or more above average; for women the equivalent bands sit roughly eight points higher because of essential fat in breast and reproductive tissue. Below about 3% for men and 12% for women is dangerously low and associated with hormonal disruption.
If you have no tape measure, the Deurenberg equation estimates body fat from BMI, age and sex: 1.2 x BMI plus 0.23 x age, minus 10.8 for men, minus 5.4. It is convenient but noticeably less reliable for muscular or older people, since it cannot see where the weight actually sits.
Accuracy and when to get a real measurement#
Both methods are estimates, typically within three to four percentage points of a DEXA scan for average builds and further off at the extremes. Neither is a diagnosis, and neither replaces clinical assessment. Trends matter far more than any single reading, so re-measure under identical conditions every few weeks rather than daily.
If you want precision for medical or competitive reasons, DEXA, air displacement plethysmography or a trained technician with calipers will all beat a tape measure. Talk to a doctor before pursuing very low body fat, and seek help promptly if pursuing a number is affecting how you eat.
Worked examples#
Male, 180 cm, 90 cm waist, 38 cm neck, 80 kg
Working the male Navy equation by hand, then converting to fat and lean mass.
- waist − neck = 90 − 38 = 52 cm
- log₁₀(52) = 1.71600, and 0.19077 × 1.71600 = 0.32736
- log₁₀(180) = 2.25527, and 0.15456 × 2.25527 = 0.34857
- Denominator = 1.0324 − 0.32736 + 0.34857 = 1.05361
- 495 ÷ 1.05361 = 469.81, then 469.81 − 450 = 19.81
- Fat mass = 80 × 0.1981 = 15.8 kg; lean mass = 80 − 15.8 = 64.2 kg
About 19.8% body fat — the average band for men. If the waist had been measured at 93 cm instead, the estimate would rise to roughly 21.6%, which shows how much rides on tape placement.
Female, 165 cm, 75 cm waist, 98 cm hip, 32 cm neck, 65 kg
The female equation, which adds hip girth to the waist term.
- waist + hip − neck = 75 + 98 − 32 = 141 cm
- log₁₀(141) = 2.14922, and 0.35004 × 2.14922 = 0.75231
- log₁₀(165) = 2.21748, and 0.221 × 2.21748 = 0.49006
- Denominator = 1.29579 − 0.75231 + 0.49006 = 1.03354
- 495 ÷ 1.03354 = 478.94, then 478.94 − 450 = 28.94
- Fat mass = 65 × 0.2894 = 18.8 kg; lean mass = 65 − 18.8 = 46.2 kg
About 28.9% body fat — the average band for women. Note this sits nine points above the male example while describing a comparable level of leanness, because women carry substantially more essential fat.
Reference tables#
| Category | Men | Women |
|---|---|---|
| Essential fat | Below 6% | Below 14% |
| Athletic | 6 – 13% | 14 – 20% |
| Fitness | 14 – 17% | 21 – 24% |
| Average | 18 – 24% | 25 – 31% |
| Above average | 25% and over | 32% and over |
Essential fat — the minimum needed for hormonal, neurological and reproductive function — is about 2–5% in men and 10–13% in women. Sustained levels below that are associated with hormonal disruption, menstrual irregularity and bone loss. These bands describe distributions, not diagnoses.
| Site | Landmark | Posture and breathing |
|---|---|---|
| Neck (both sexes) | Immediately below the larynx, sloping slightly down at the front | Stand tall, eyes forward, chin neutral — never tucked |
| Waist (men) | Horizontal at navel level | Arms at sides, read at the end of a normal exhale |
| Waist (women) | Narrowest point of the torso, between lowest rib and hip bone | Arms at sides, read at the end of a normal exhale |
| Hip (women) | Widest circumference of the buttocks | Feet together, tape level and parallel to the floor |
| Height | Heels together against a wall, to the crown of the head | Shoes off, looking straight ahead |
Round to the nearest 0.5 cm and average three readings per site. Consistency between sessions matters more than absolute precision.
| Method | Typical spread vs DEXA | Practicality |
|---|---|---|
| DEXA scan | Reference method (±1–2 points between scans) | Clinic or research facility, paid appointment |
| Hydrostatic weighing | About ±2–3 points | Specialist lab, requires full underwater exhale |
| Air displacement (Bod Pod) | About ±2–3 points | Specialist facility |
| Skinfold calipers, trained tester | About ±3–4 points | Cheap, but highly tester-dependent |
| US Navy tape method | About ±3–4 points | Free, needs only a tape measure |
| Bioelectrical impedance scales | About ±4–5 points, shifts with hydration | Convenient, poor for absolute values |
| Deurenberg BMI-based estimate | Widest spread; poor for muscular and older people | Needs no measurements beyond height, weight, age |
Figures are indicative ranges reported across validation studies, not guarantees for any individual. Every method here estimates fat mass from something else — none of them weigh fat directly.
Common mistakes#
- Bracing, sucking in or holding a breath at the waistWaist girth is the dominant term in both equations. Tightening the abdomen can shrink the reading by 3–4 cm, which flatters the estimate by roughly the same number of percentage points and makes any comparison with a later measurement meaningless.
- Measuring at different times of dayWaist circumference is measurably larger after meals and in the evening, and fluid retention shifts it too. Comparing a morning fasted reading with an evening post-dinner one can invent or hide two percentage points of change that never happened.
- Using the male protocol on a female body or vice versaThe two equations use different constants, different waist landmarks, and only one includes the hip. Feeding a navel-level waist into the female formula, or omitting the hip, produces a result that is wrong by well over the method's stated error margin.
- Chasing a very low body fat numberBelow roughly 5% in men and 13% in women you are into essential fat, and sustained levels there are associated with hormonal disruption, loss of menstrual cycles and reduced bone density. If a body fat target is starting to shape how you eat or train in ways that worry you, that is a reason to speak to a doctor.
Frequently asked questions#
How accurate is the US Navy body fat formula?
It is usually within three to four percentage points of a DEXA scan for people of average build. Measurement technique is the biggest source of error, so keep the tape position consistent.
What is a healthy body fat percentage?
Broadly 14-24% for men and 21-32% for women, with athletes lower. Essential fat is about 3% for men and 12% for women, and going below that carries real health risks.
Why do women need hip measurements?
The female version of the Navy equation includes hip girth because women store proportionally more fat around the hips and thighs, and waist alone predicts poorly.
Can I lose fat without losing weight?
Yes. Gaining muscle while losing fat can leave the scale flat, which is exactly why tracking body fat or measurements alongside weight is useful.
Key terms#
- Body fat percentage
- Fat mass expressed as a share of total body mass. Unlike BMI it distinguishes fat from muscle, bone and water, which is why it tracks body composition changes that the scale hides.
- Lean body mass
- Everything that is not fat — skeletal muscle, bone, organs and body water. Total weight minus fat mass. It is the metabolically active tissue that determines much of your resting energy expenditure.
- Essential fat
- The minimum body fat required for normal physiological function, roughly 2–5% in men and 10–13% in women. The higher female figure reflects fat in breast, hip and reproductive tissue.
- Circumference (anthropometric) method
- Any technique that predicts body composition from tape measurements and height. The Navy equations are the best-known example, fitted by regression against hydrostatic weighing.
- DEXA
- Dual-energy X-ray absorptiometry. A scan that separates fat, lean tissue and bone mineral by their differing X-ray absorption, and the usual reference standard for validating simpler methods.
- Deurenberg equation
- A 1991 formula estimating body fat from BMI, age and sex: 1.2 × BMI + 0.23 × age − 10.8 (men only) − 5.4. Convenient when no tape is available, but it inherits every one of BMI's blind spots.
Sources#
- Shake CL et al., 'Predicting percent body fat from circumference measurements' (Military Medicine, 1993) — validation of the Navy circumference equations — PubMed
- Deurenberg P et al., 'Body mass index as a measure of body fatness: age- and sex-specific prediction formulas' (Br J Nutr, 1991) — PubMed
- Definitions, Classification and Epidemiology of Obesity — including body composition assessment methods — NIH / NCBI Bookshelf (Endotext)
- Overweight and obesity — definition and facts — NIH / NIDDK
Figures last checked .
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