The neck measurement is the smallest input in the U.S. Navy body fat formula and the one most often taken incorrectly. A centimetre of error at the neck can move the estimate by a percentage point or more. Here is the placement, the tension and the mistakes to avoid.
The U.S. Navy circumference method estimates body fat from the difference between the waist and the neck, adjusted for height. The logic is that a larger waist relative to the neck suggests more abdominal fat, while a thicker neck suggests a larger frame and more lean mass. For women, the hip is added to the equation.
The method was developed for military fitness screening, where a tape measure is cheaper and faster than calipers or underwater weighing. It is not a direct measurement of fat. It is a prediction equation, and its accuracy depends on the inputs being taken consistently.
The full equations are in the Navy body fat formula explained. This guide focuses on the neck measurement itself.
Measure just below the larynx — the Adam's apple — at the narrowest part of the neck. The tape should sit at the level of the thyroid cartilage, not at the base of the neck and not at the jawline.
Keep the tape level at the back and let it slope slightly downward at the front, following the natural angle of the neck. This is the placement specified by the Navy method. A tape that is horizontal all the way around tends to ride up at the front.
If you have a very short neck or a prominent larynx, the “just below” landmark can be hard to reproduce. In that case, use the narrowest visible circumference of the neck and note the method. Consistency matters more than a perfect landmark.
The waist-to-neck difference is used inside a logarithm, so small changes at the neck can have a noticeable effect. A 2 cm error at the neck can shift the estimated body fat by roughly one to two percentage points for an average-sized adult. That is within the method's own error range, but it matters if you are comparing readings over time.
This is why the same tape, the same landmark and the same tension matter. If you measure the neck tightly one month and loosely the next, the trend will reflect the tape technique rather than your body.
Rule of thumb: if your neck reading changes by more than 1.5 cm between two sessions without a clear reason, re-measure before trusting the body fat trend.
Measuring at the base of the neck. This captures the shoulders and upper chest, not the neck. The reading will be too large and the body fat estimate too low.
Measuring over a collar or hoodie. Clothing adds circumference. Measure on skin or over a thin shirt that you will wear consistently.
Flexing or turning the head. Neck muscles change the circumference. Look straight ahead and keep the neck relaxed.
Pulling the tape tight. Compressing the skin reduces the reading. Snug, not tight.
Swallowing during the measurement. The larynx moves and the tape can shift. Read at the end of a normal exhale.
Using a different landmark each time. Pick a reproducible point and stick to it. If you use “just below the larynx”, use it every time.
For the Navy formula, men need height, neck and waist. Women need height, neck, waist and hip. The waist is measured at the narrowest point or at the midpoint between the lowest rib and the hip bone; the hip at the widest point of the seat. The neck is the only measurement taken above the shoulders.
If you are using the body shape calculator, enter the neck, waist and hip and the tool will estimate body fat and report the uncertainty. It also calculates BMI, a healthy weight range, waist-to-hip ratio and body shape from the same inputs. You can see the formula for each result rather than a black-box number.
For the waist and hip technique, see how to measure your waist and hips. For the equations and a worked example, see the Navy body fat formula.
The Navy circumference method typically lands within about 3–4 percentage points of a DEXA scan for many adults, but individual error can be larger. Very muscular people, very lean people, older adults and people with a lot of abdominal fat may be further off. The method also assumes a typical fat distribution, which not everyone has.
Treat the result as an estimate with a range, not a precise measurement. The calculator reports an uncertainty of plus or minus four percentage points for this reason. A reading of 24% is better read as “roughly 20–28%”, and a change of one or two points between sessions may be noise.
If you need a precise body composition measurement, DEXA, hydrostatic weighing or a properly conducted caliper test are more accurate. A tape estimate is useful for tracking a trend and for a rough sense of where you are, not for a clinical diagnosis.
The neck circumference is not a direct measure of body fat. It is a proxy for frame size and upper-body lean mass, which helps the equation correct for the fact that a larger waist may reflect a larger skeleton rather than more fat. In the men's formula, the difference between waist and neck is the main driver; in the women's formula, hip is added because fat distribution differs.
This is also why the method can mislead in people with unusual proportions. A bodybuilder with a large neck and a modest waist may get an estimate that is too low. A person with a slender neck and a large waist may get an estimate that is too high. The equation is a population-level approximation, not a personal scan.
The placement is the same for both sexes. The difference is in the equation: the men's formula uses neck, waist and height, while the women's formula adds hip. That means the neck measurement is the only input that is identical across the two equations.
For both sexes, the neck should be measured at the narrowest point below the larynx. Do not use the collar size from a shirt; collar sizing is based on a different measurement and includes ease. A 16-inch collar does not mean a 16-inch neck circumference.
If you have a very thick neck or a very slender one, the equation still applies, but the estimate may be less accurate. The method was calibrated on a military population that may not match your body type. Treat the result as a starting point.
A beard can add apparent circumference if the tape sits over hair rather than skin. Part the beard or measure at a point where the tape can touch the skin. If that is not possible, keep the same method each time and accept that the reading includes the beard.
Turtlenecks, scarves and hoodies add fabric thickness. Measure on bare skin or over a thin shirt that you will wear consistently. A collared shirt should be unbuttoned at the neck so the tape can sit flat.
Jewellery, a lanyard or a tie should be removed. Even a thin chain can lift the tape by a millimetre, which is small but avoidable. The goal is a repeatable measurement, not a perfect one.
Before you record a baseline, practise the measurement three times. Measure, wait a minute, measure again, and compare. If the readings are within 0.5 cm, your technique is repeatable. If they vary by more than 1 cm, check the landmark, the tape angle and your neck tension.
Once you have a repeatable method, record the average of two readings. Re-measure at the same time of day, ideally in the morning, and avoid measuring right after exercise or a hot shower. The neck can change slightly with posture and hydration, so consistency matters more than chasing a decimal.
Just below the larynx, at the narrowest part of the neck, with the tape sloping slightly downward at the front. Keep the neck relaxed and the tape snug without compressing the skin.
Yes. The women's equation uses neck, waist, hip and height. The men's equation uses neck, waist and height. The neck placement is the same.
The estimate depends on the waist-to-neck difference. A change in neck or waist measurement, hydration, posture or tape placement can move the result. Re-measure with the same method before assuming your body composition changed.
This is an editorial reference, not medical advice. Body shape and body fat estimates describe proportions; they do not diagnose health.
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