The US Navy body fat method is the most widely used way to estimate body fat without any special equipment. You need a tape measure, two or three measurements, and your height.
It is not the most accurate method available. It is the most accessible accurate-enough one, and it is very good at the thing that matters most: showing whether your body fat is going up or down over time.
Where it comes from
The formula was developed in the 1980s by researchers at the Naval Health Research Center, led by James Hodgdon and Mark Beckett. The Navy needed a way to screen personnel for body composition that was quick, cheap and consistent across thousands of people, without hydrostatic weighing tanks.
They measured body density directly in hundreds of sailors, then looked for the combination of simple measurements that best predicted it. For men, waist and neck circumference plus height turned out to be enough. For women, adding hip circumference improved the prediction.
The same basic equations are still used by the US military today.
The formulas
All measurements are in centimetres.
Men:
Body fat % = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
Women:
Body fat % = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450
The equations first estimate body density, then convert density to body fat percentage using the Siri equation, which is where the 495 and 450 come from.
There is also an inch-based version with different constants. It gives the same answer; use whichever matches your tape.
Rather than do the logarithms by hand: Navy body fat calculator.
A worked example
A man who is 178 cm tall, with a 90 cm waist and a 38 cm neck:
- Waist − neck = 90 − 38 = 52
- log₁₀(52) = 1.716
- log₁₀(178) = 2.250
- Denominator = 1.0324 − (0.19077 × 1.716) + (0.15456 × 2.250) = 1.0324 − 0.3274 + 0.3478 = 1.0528
- 495 ÷ 1.0528 = 470.2
- 470.2 − 450 = about 20% body fat
For a man that falls in the “average” range. If his waist dropped to 85 cm with no other change, the same calculation gives about 16.5%.
Why neck, waist and hip?
Waist is the main signal. It is where much of the body's fat is stored, especially visceral fat around the organs, and it changes most as fat is gained or lost.
Neck acts as a correction for frame size. A larger neck usually indicates a larger frame and more lean mass, so subtracting it from the waist separates “big” from “carrying fat”.
Hip is added for women because women typically store more fat around the hips and thighs, and waist alone underestimates body fat in women.
Height scales everything: the same waist means more on a shorter person than on a taller one.
How to measure properly
Most of the error in the Navy method comes from measuring, not from the formula. A 1 cm difference in waist changes the result by roughly one percentage point.
- Neck: just below the larynx (Adam's apple), with the tape sloping slightly downward at the front. Do not flex, and do not let your head tilt.
- Waist, men: horizontally at the level of the navel.
- Waist, women: at the narrowest point of the torso, usually a little above the navel.
- Hip, women: at the widest point of the buttocks, with feet together.
- Always: relaxed, standing straight, at the end of a normal breath out. The tape snug but not compressing the skin.
Measure three times and use the average. Measure at the same time of day each time (first thing in the morning is best) and ideally have someone else hold the tape.
How accurate is it?
Compared with DEXA scans, the Navy method typically comes within 3–4 percentage points for most people. Some studies find it better, some worse; accuracy depends heavily on how carefully measurements are taken.
It is least accurate for:
- Very lean people, where it tends to overestimate.
- People with a lot of body fat, where it can underestimate.
- People with an unusual build: a very thick neck from training, or fat stored mainly in the limbs.
- Some ethnic groups it was not developed on. South Asian adults, for example, tend to carry more body fat at the same measurements, so the formula can read low.
How it compares with other methods
| Method | Typical accuracy | Cost and access |
|---|---|---|
| DEXA scan | ±1–2% | Clinic, paid |
| Hydrostatic weighing | ±2% | Rare, lab only |
| Skinfold calipers (trained tester) | ±3–4% | Cheap; skill-dependent |
| US Navy tape method | ±3–4% | Free, a tape measure |
| Bathroom scale (bioimpedance) | ±4–8%, swings with hydration | Cheap; easy |
| BMI | Does not measure fat | Free |
For tracking change over months, the tape method is a better choice than a bioimpedance scale. Scale readings can move several points in a day with hydration; your waist does not.
What the result means
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Above average | 25%+ | 32%+ |
Women carry more essential fat than men for reproductive and hormonal reasons. It is not a fitness gap. Anything at or below the essential range is a medical concern, not a goal.
The best way to use it
Measure once a month, under the same conditions, and watch the trend. If your weight has stalled but your Navy body fat estimate is dropping, you are losing fat and probably holding or gaining muscle, which is the best kind of stall.
Pair it with waist-to-height ratio, which uses one of the same measurements and is a strong health-risk marker in its own right.
Where BetterCal fits
Body composition changes slowly and follows what you eat, especially protein. BetterCal makes the eating side easy to track: type or speak a meal and it is logged with calories, protein, carbs and fat. Repeat meals are a single tap.
Log a meal the way you would write it down. BetterCal turns a plain sentence, spoken or typed, into calories and macros. Free to start.
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Frequently asked questions
What is the Navy body fat formula?
For men: 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450. For women: 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.221 × log10(height)) − 450. All measurements in centimetres.
How accurate is the Navy body fat calculator?
Usually within 3–4 percentage points of a DEXA scan when measurements are taken carefully. It is less accurate for very lean or very heavy people, but it is reliable for tracking change over time.
Why does the Navy method use neck measurement?
The neck is a proxy for frame size and lean mass. Subtracting it from the waist helps separate a large frame from a large amount of body fat.
Is the Navy method better than BMI?
For estimating body fat, yes. BMI only uses height and weight, so it cannot tell muscle from fat. The Navy method uses waist measurement, which tracks fat much more closely.
How often should I measure body fat?
Once every two to four weeks is enough. Body fat changes slowly, and more frequent measurements mostly pick up measuring error.
Related: Navy body fat calculator · BMI calculator · goal weight calculator
