A Free Calculator · US Navy Circumference Method · Updated 2026
What is your body fat percentage, by the Navy tape method?
The US Navy circumference formula estimates body fat from three tape measurements —
waist, neck, and height for men; waist, neck, hip, and height for women. It takes
about two minutes with a soft tape measure. The result is an estimate accurate to
roughly ±3–4%, not a clinical measurement. Every formula is shown; nothing
is hidden.
US Navy formula·Male & female versions·Estimate only — not a medical assessment
Important — read before using
This is an estimate from the US Navy tape-measure (circumference) method, accurate
to roughly ±3–4%. It is not a medical diagnosis or health
assessment. Laboratory methods (DEXA, hydrostatic weighing) differ. The reference
ranges shown are general fitness references, not health classifications. Do not use this
result to self-diagnose a condition or make a medical decision — consult a healthcare
provider for that.
Select your sex, enter your measurements in inches, and the result updates as you type. Women need a hip measurement; men do not. See the measurement guide below if you're unsure where to place the tape.
Sex & measurements (inches)
The formula uses different coefficients for male and female — the female version adds a hip measurement.
in
In inches. 5′10″ = 70 in. (1 ft = 12 in.)
in
Measured at the navel (belly button), horizontally, at normal exhale. Not at the narrowest point.
in
Measured just below the larynx (Adam's apple), sloping slightly downward to the front.
in
Measured at the widest point of the hips and buttocks, horizontally.
Estimated body fat:
Estimated body fat
US Navy tape-measure method
Method
Accuracy roughly ±3–4% vs lab methods
General category
Key measurement
The formulas, in full
Nothing is a black box. These are the exact equations the tool runs — the same
arithmetic you could verify with a calculator. All measurements must be in inches.
Coefficients are from the original US Navy regression derived by Hodgdon and Beckett
(1984) and used in Navy Physical Readiness standards.
How each number is derived
Male formula — waist, neck, height (all in inches)
Female formula — waist, hip, neck, height (all in inches)
%BF = 163.205 × log₁₀(waist + hip − neck)
− 97.684 × log₁₀(height)
− 78.387
The hip measurement adds predictive power for female fat
distribution — the male formula omits it because male fat
distribution is primarily abdominal.
Validate: (waist + hip − neck) must be > 0 before taking log.
Why the formulas differ by sex
Both equations were derived via regression from a large
population sample. The coefficients (86.010, 70.041, etc.)
are not physical constants — they are the fitted values
that minimized prediction error for each sex's data.
The logarithms capture the non-linear relationship between
circumference measurements and true body fat.
General body fat reference ranges
The table below shows general fitness-industry reference categories. These are
not medical or health classifications — they are contextual labels
compiled from published exercise science literature to give a rough sense of where
a number falls. Healthy body fat levels vary with age, genetics, and individual
health status. A category name is not a diagnosis. Methods like DEXA and calipers
often produce different numbers than the Navy tape method.
General category
Men (approx. %)
Women (approx. %)
Context note
Essential fat
under 6%
under 14%
Minimum fat required for physiological function (typically ~2–5% in men, ~10–13% in women). Below the essential level is associated with serious health risk. Women carry higher essential fat due to reproductive physiology.
Athletic
6–14%
14–21%
Typical range for competitive athletes and those with high training volumes. Lean appearance, visible muscle definition. Not a target for general fitness.
Fitness
14–18%
21–25%
Common in fit, active adults. Good physical capacity without competition-level leanness. Many fitness professionals fall here.
Average
18–25%
25–32%
Reflects typical ranges in the general population. Not inherently problematic — this bracket covers a wide variety of healthy individuals.
Above average
25%+
32%+
Above the population average. This label does not mean unhealthy — individual health depends on many factors beyond body fat percentage. Consult a healthcare provider for health assessment.
These ranges are general fitness references adapted from published exercise science sources (ACE, ACSM). They are not a medical classification or health risk score, and the Navy tape method that produces your number has an accuracy of roughly ±3–4% compared to lab methods. A result near a category boundary could reasonably belong to either adjacent category. Do not use these ranges as a medical benchmark.
What the number actually tells you — and what it doesn't
A body fat percentage from a tape measure is a useful data point, not a verdict.
Understanding what the method can and cannot do helps you use the number correctly.
Trend tracking matters more than any single reading
Because the method has roughly ±3–4% error, a single reading of 18.4% is best interpreted as "somewhere in the 14–22% range." What the method is well suited for is consistent re-measurement over weeks or months with the same technique and the same time of day. If the number is reliably trending in the direction you want, you have meaningful signal even though the absolute number is uncertain.
Measurement consistency is the biggest source of error
The formula itself is deterministic — it will give the same answer for the same inputs every time. The variation comes from the tape. Even small differences in placement (navel vs. slightly above it), tape tension, breathing phase (inhaled vs. exhaled), and time of day (morning vs. after a meal) can shift the result by several percentage points. Take measurements in the morning before eating, with consistent tape placement, and average two or three readings at each site if precision matters.
This is a fitness estimate, not a health diagnosis
The reference categories above are descriptive, not prescriptive. "Above average" body fat is not a diagnosis of any condition. Metabolic health, cardiovascular risk, and overall wellbeing depend on far more than body fat percentage — activity level, sleep, diet quality, blood markers, genetics, and age all matter. If you have concerns about your health status, speak with a clinician rather than using a tape measure to self-assess.
How to take the tape measurements correctly
The formula is only as good as the inputs. These are the standardized measurement
sites used by the US Navy method — taking them any other way will produce a
different (and incorrect) result.
Use a soft, flexible tape measure
A dressmaker's or body-measurement tape works perfectly. A rigid carpenter's tape does not flex around the body accurately. The tape should be snug against the skin — not compressing tissue, not leaving slack. A single layer of thin clothing can introduce error; measure directly on skin when possible.
Measure the waist at the navel, not the narrowest point
The US Navy protocol places the waist tape at the belly button (navel), running horizontally. This is different from the fashion convention of measuring at the waist's narrowest point, which is typically an inch or two above the navel. Using the wrong site is the single most common measurement error — it will produce a reading that is too small and underestimates body fat.
Exhale normally, then take the reading
Take the waist measurement at the end of a normal, relaxed exhale — not sucked in, not fully exhaled and contracted. Breath-holding adds variability. Most people's waist measurement fluctuates 0.5–1 inch across a breath cycle; the exhaled position is the standard reference point.
Measure the neck just below the larynx
Place the tape just below the larynx (Adam's apple for men; the corresponding cartilage for women), with the tape angled slightly downward toward the front. The neck should be relaxed and upright — tilting it or tensing the muscles changes the circumference. For most people this measurement doesn't change much day-to-day, so it's the waist (and hip, for women) that drives most of the variation.
Women: measure the hip at its widest horizontal point
Stand with feet together. Place the tape around the widest part of the hips and buttocks — the maximum circumference — keeping it horizontal. This is usually at or near the level of the greater trochanter (the bony prominence on the outer hip). It is not the same as the "hip bone" that protrudes above. Having a second person confirm the tape is level and at the widest point improves accuracy.
Average two or three readings per site
Remove the tape, re-position, and measure again. If the two readings agree within about 0.25 inches, average them. If they differ more, take a third reading and average all three. Repeating the measurement removes the effect of slightly imperfect tape placement and gives you a more stable input.
Where to buy
Got your numbers? Here's where to pick up what you need:
The terms that appear in body fat discussions — in plain English, without the
sales framing.
Body fat percentage (%BF)
The fraction of total body mass that is fat tissue, expressed as a percentage. The remainder is lean mass — muscle, bone, water, and organs. Methods of measuring it include DEXA, hydrostatic weighing, air displacement plethysmography (Bod Pod), skinfold calipers, and circumference-based formulas like the US Navy method. Each has different accuracy and accessibility tradeoffs.
Lean mass
Everything that is not fat: muscle, bone, water, connective tissue, and organs. Body fat percentage and lean mass are complementary — if you know one and your total weight, you can calculate the other. Two people at the same weight can have very different body compositions and thus different fat and lean mass figures.
DEXA (dual-energy X-ray absorptiometry)
A clinical imaging method that uses two low-dose X-ray beams to distinguish bone mineral, lean tissue, and fat tissue. Considered one of the most accurate body-composition methods available outside a research setting, with error of roughly ±1–2%. Typically done at a medical facility or university sports science lab. The Navy tape method is compared against DEXA and similar methods to characterize its accuracy.
Hydrostatic (underwater) weighing
A historical gold-standard method that estimates body density by weighing a person fully submerged in water, then applying Archimedes' principle. Dense bone and muscle sink more; fat is less dense and increases buoyancy. Accurate when lung volume is controlled, but inconvenient and increasingly replaced by DEXA for research use.
Circumference method
Any body fat estimation approach that uses tape measurements (circumferences) at specific body sites as the only input — no weight scale required. The US Navy formula is the most widely used circumference method. It is population-based: the regression coefficients were derived from a large sample, so the formula is more accurate for people similar to that population than for outliers.
Essential fat
The minimum body fat required for normal physiological function: cushioning organs, insulating the body, and (in women) supporting reproductive hormones. Men typically have about 2–5% essential fat; women about 10–13%, reflecting the demands of reproductive physiology. Going below these levels is associated with serious health consequences.
Regression formula
A statistical model that relates one measured variable (body fat, estimated from a scan or direct method) to other, easier-to-measure variables (circumferences) using coefficients fitted to a population dataset. The US Navy formula coefficients are the result of minimizing prediction error across that population. The formula is empirical — it works because it fit the data, not because circumferences and fat have a theoretical mathematical relationship.
Frequently asked
The US Navy circumference method is generally cited as accurate to roughly ±3–4 percentage points compared to laboratory-grade methods such as DEXA or hydrostatic weighing. A result of 18% from this calculator could represent a true body fat of 14–22% in a lab setting. That range makes it a reasonable tool for tracking trends over time — if you measure consistently and the number moves in a direction, that trend is more meaningful than the absolute figure. For clinical purposes, more precise methods are used. Do not use this result to diagnose a health condition.
The US Navy formula was derived from regression analysis fitting tape measurements to body-composition reference data from a large population. Logarithms capture the non-linear relationship between circumference measurements and true body fat — the same absolute change in waist circumference means something different at different body sizes. The base-10 logarithms of the circumference differences and height are inputs to a linear equation whose coefficients were set by the regression. The formula is empirical, not theoretical: it works because it fits the population data it was built on.
Women typically carry a greater proportion of body fat in the hip and glute region compared to men, so a hip measurement adds predictive power that waist and neck alone cannot capture. The female formula was derived from the same regression process as the male formula, but fit to female population data where hip circumference was found to be a meaningful predictor. Omitting it — as the male formula does, because male fat distribution is more centrally abdominal — would reduce accuracy for women significantly.
For the US Navy method, both men and women measure the waist at the navel (belly button), not at the narrowest point. This differs from the fashion or clothing convention of measuring at the narrowest point above the navel — using the wrong location will produce an incorrect result. The tape should be horizontal, snug but not compressing tissue, and the measurement taken at a normal exhale. See the step-by-step guide above for details.
BMI (body mass index) uses only height and weight — it has no information about how much of your weight is fat versus muscle, bone, or water. A muscular person can have a high BMI with very low body fat; someone with low muscle mass can have a normal BMI with high body fat. The Navy formula uses circumference measurements that correlate with fat distribution and therefore provides a better — though still imperfect — estimate of actual fat percentage. Neither BMI nor the Navy formula is a clinical measurement; both are population-level screening tools.
DEXA is considered one of the most accurate body-composition methods outside a research setting, with error of roughly ±1–2%. Hydrostatic (underwater) weighing was a historical gold standard. Skinfold calipers, done by an experienced practitioner at standardized sites, typically achieve ±3–4%. The Navy tape method is in the same ±3–4% ballpark as calipers and is widely used because it requires only a tape measure. All consumer methods are less accurate than DEXA. If your goal is precise body composition for medical or performance purposes, a DEXA scan is the appropriate tool.
The formulas shown on this page are calibrated to inches. If you measure in centimeters, divide each measurement by 2.54 to convert to inches before entering it. The calculator accepts inches by default. Converting all inputs consistently will give you the correct result — mixing units (some in centimeters, some in inches) will not.
The ranges on this page (Essential, Athletic, Fitness, Average, Above Average) are general fitness-industry reference categories compiled from published exercise science sources. They describe where most measured people fall, not what is medically healthy or unhealthy for a specific individual. Healthy body fat levels vary with age, sex, genetics, and individual health status. A range labeled "Above Average" does not mean unhealthy, and "Athletic" does not mean optimal for you. These labels exist only to give context to a number — they are not a diagnosis, a health risk score, or a medical recommendation. Speak with a healthcare provider if you have questions about your body composition and health.
Common mistakes
The Hodgdon & Beckett formula (US Navy method) is deterministic — the same
inputs always produce the same output. All the error lives in the tape, not the
math. These are the measurement mistakes that produce unreliable results.
Measuring the waist at the narrowest point instead of the navel
The US Navy protocol places the tape at the belly button (navel), not at the waist's narrowest point. The fashion convention — measuring an inch or two above the navel where the waist narrows — produces a smaller circumference and underestimates body fat. This is the single most common measurement error. The protocol is navel, horizontal, every time.
Taking one measurement and trusting it
A single tape reading at any site can be off by a quarter-inch or more depending on exact placement, tension, and breathing. The standard approach is to measure each site twice, confirm the readings agree within about 0.25 inches, and average them. If they diverge more, take a third reading and average all three. One measurement is a data point; two or three agreeing measurements are a result.
Measuring at different times of day and comparing the results
Body circumferences fluctuate throughout the day — waist especially, due to meals, hydration, and bloating. A morning measurement before eating can be an inch smaller than an evening measurement after dinner, shifting the body fat estimate by several percentage points. Choose a consistent measurement time (morning before eating is standard) and always measure at the same time when tracking progress.
Treating a single result as an accurate absolute number
The Navy tape method has roughly ±3–4% error compared to lab methods like DEXA. A reading of 18% is best understood as "somewhere between about 14% and 22%." The method's real value is tracking relative change over weeks or months with consistent technique — not pinpointing an exact body fat percentage from one session.