Body Fat Calculator - US Navy / Hodgdon–Beckett Tape Method

A Navy body fat calculator answers a field question: given standing height and a few tape circumferences, what percentage does the Hodgdon–Beckett circumference method assign? The equations were published for U.S. Navy use in the 1980s and remain the arithmetic behind many “US Navy body fat” web tools. They are not a dual-energy X-ray absorptiometry (DEXA) scan, not air-displacement plethysmography, not hydrostatic weighing, and not a medical diagnosis of obesity or of an eating disorder.

The default male example on this page is 70 inches tall, 16 inch neck, and 33 inch abdomen at the navel. Converted through the male equation that is 86.010 × log10(33 − 16) − 70.041 × log10(70) + 36.76 = 86.010 × log10(17) − 70.041 × log10(70) + 36.76 ≈ 13.36%, which people often round to 13.4%. That identity is here so you can check the JavaScript, not because 13.4% is a goal or a standard.

Men need three lengths: height, neck, and abdomen at the navel. Women need four: height, neck, waist, and hip. The male logarithm sees (abdomen − neck). The female logarithm sees (waist + hip − neck). If either difference is zero or negative, log10 is not defined for this method and this page refuses the result. A neck larger than the trunk sites is a measurement error, not a “negative body fat.”

Typical disagreement versus DEXA for circumference methods is often about ±3–5 percentage points in mixed adult samples, and can be worse with unusual fat patterning, very large muscle mass, pregnancy, edema, or a tape pulled like a tourniquet. Honest use means treating 13.36% as “the Navy equation on these tapes,” not “my true adiposity to two decimals.”

This is not medical advice. If you want a height-and-weight screening index instead of tapes, use the BMI calculator. If you want lean mass from weight and height regressions, use the lean body mass calculator. A military-framed write-up of the same Hodgdon–Beckett math is on the Army body fat calculator- still not an official tape test.

1. Choose male or female. The equations are different; swapping labels without swapping sites is wrong.
2. Choose imperial inches (the published fit) or metric centimetres. Centimetres are divided by 2.54 before any log10. Never drop centimetres into an inches formula.
3. Measure standing height without shoes. Measure neck just below the larynx, tape sloping slightly downward to the front, not choking. For men, measure abdomen at the navel at the end of a normal breath, not sucked in. For women, measure waist at the typical narrowest site used in Navy-style protocols and hip at the largest protrusion of the buttocks.
4. Read the percentage, copy it if you need a note, and remember the error band. Inputs stay in this browser for up to 30 days and are never uploaded.

Default male: abdomen − neck = 33 − 16 = 17. log10(17) ≈ 1.23044892. log10(70) ≈ 1.84509804. 86.010 × 1.23044892 ≈ 105.8316. 70.041 × 1.84509804 ≈ 129.2332. 105.8316 − 129.2332 + 36.76 ≈ 13.36. Displayed as 13.36%. The common spoken rounding is 13.4%. This implementation uses JavaScript Math.log10, not a change-of-base approximation you have to remember, and not eval.

Metric check of the same body: 70 in = 177.8 cm, 16 in = 40.64 cm, 33 in = 83.82 cm. Dividing each by 2.54 recovers the inches, so the percentage must match. If a site converted centimetres incorrectly (for example treating cm as inches), log10(83.82 − 40.64) would describe a different person.

Female arithmetic is the same idea with a four-site log argument. A worked illustration: 64 in height, 13 in neck, 28 in waist, 38 in hip → log argument 28 + 38 − 13 = 53. 163.205 × log10(53) − 97.684 × log10(64) − 78.387 is the estimate for those tapes. Change any site by half an inch and the log moves; that sensitivity is why tape tension and landmark choice dominate “accuracy” conversations more than extra display digits.

Why subtract neck? The regression is trying to separate a trunk girth that tracks adipose tissue from a neck girth that tracks leaner geometry in the original samples. It is an empirical trick, not a proof that fat lives only at the navel. Two people can share abdomen and height and differ in visceral versus subcutaneous fat in ways no tape sees.

A steel or fiberglass tape laid on skin, parallel to the floor at the landmark, without compressing the tissue, is closer to how these equations were trained than a clothing measurement or a flexed “gym pump” abdomen. Repeat the site three times and average if you care about week-to-week noise. Measure at the same time of day; a large meal and a full bladder move the navel tape.

Strength athletes often get a higher Navy percentage than their DEXA fat mass would suggest, or the reverse, depending on where muscle sits relative to the landmarks. The method never sees arms, thighs, or intramuscular fat. Older adults can carry visceral fat with a modest abdomen tape if posture and rib geometry differ from the 1980s sailor samples. Pregnancy, ascites, and amputation are out of scope; do not force the equation.

Popular “essential / athletic / average / obese” body-fat tables (ACE and similar) are educational cartoons, not Navy regulations and not WHO diagnoses. This calculator does not stamp a disease name on 13.36% or on 35%. BMI categories on the BMI calculator are a different instrument (kg/m²). Mixing a tape percentage with a BMI band as if they were one lab panel is a category error.

Calipers (Jackson–Pollock and others) and bioimpedance scales are yet more methods. They will not match this page. If you already have a BF% from somewhere and want LBM = weight × (1 − BF/100), that optional check lives on the lean body mass calculator, labeled as coming from body-fat %, not from Boer.

James Hodgdon, Marcie Beckett, and colleagues at the Naval Health Research Center fitted circumference models because the fleet needed a cheap, repeatable screen that did not require a tank or an X-ray. The male and female coefficients on this page are the common “Navy method” form used in countless later DoD and web implementations. Coefficients are not sacred biology; they are a 1980s sample’s best linear combination of log girths.

Later Department of Defense instructions and service regulations reused the same family of equations with specified tape sites and administrative rounding. That is why the Army body fat calculator can show the same 13.36% on 70 / 16 / 33 and still must disclaim that it is not an AR 600-9 test, not a promotion board, and not a retention decision. Regulations also publish maximum allowable percentages by age and sex; those tables change and are deliberately not encoded here.

Search traffic clusters on “Navy body fat formula,” “body fat percentage calculator inches,” and “is 15% body fat good.” The honest answers: the formula is the log10 circumference pair above; inches are required inside the logs (this page converts cm); whether 15% is “good” is not a question a website should grade. Health, sport, and military standards are different jobs.

Related planning tools are not substitutes: BMR, calories, macros, protein, and body surface area (Mosteller m², not fat %). Stigma and compulsive checking are harms. If food or body measurements are taking over your life, contact a clinician. A tape calculator cannot diagnose an eating disorder, and we will not pretend it can.

Extra worked males (inches, navel abdomen): 72 / 15.5 / 34 → log arg 18.5, about 14.5%. 68 / 16.5 / 38 → log arg 21.5, about 20.4%. 74 / 17 / 32 → log arg 15, about 10.1%. Those are equation outputs, not DEXA. If abdomen − neck ≤ 0, the page errors instead of printing nonsense from log10 of a non-positive number.

Landmark error dominates coefficient error. If the male abdomen tape rides an inch above the navel one week and an inch below the next, log10(abdomen − neck) moves even when adipose tissue did not. Neck tape that creeps up under the chin or down onto the traps changes the subtracted term. Female hip tape that captures the gluteal fold versus the widest point is a different argument to log10. Write down the landmark in words the first time you measure, then reuse the same sentence. A photo of tape placement (for your own records, not for this site - nothing is uploaded) beats memory.

Breathing and gut contents are not “cheating the Navy formula”; they are part of why a field method has a wide error bar. End-expiration at the navel is the usual instruction in circumference protocols. A pumped abdomen after a large dinner is a different geometry. Sodium, the menstrual cycle, creatine loading, and alcohol can move waist and hip by amounts that look like fat loss on a two-decimal display. If you track, use a weekly median of several morning tapes, not a single heroic reading after a workout.

Bioelectrical impedance (BIA) bathroom scales inject a small current and infer a body-water compartment, then guess fat from that. They are sensitive to hydration, electrode quality, and the vendor’s unpublished regression. Jackson–Pollock and similar skinfold methods pinch subcutaneous fat at named sites and use a density equation. Neither is Hodgdon–Beckett. If you switch methods mid-diet, you have changed instruments, not necessarily changed fat mass. This calculator will not “convert” a BIA percentage into a Navy percentage.

Female-specific honesty: the four-site equation was fitted on adult women in the original naval samples, not on adolescents, not on pregnancy, and not on people with substantial breast-reduction or reconstruction geometry that changes how waist and hip sit. Postpartum abdominal laxity can inflate a waist tape relative to DEXA fat. The tool still does the log if you type numbers; the interpretation is yours and a clinician’s, not a website’s.

Male-specific honesty: “abdomen at navel” is not “smallest waist.” Many men have a navel tape larger than the narrowest belt line. Using the fashion waist in the male equation understates the log argument and prints a flattering, wrong percentage. The default 33 in abdomen on a 70 in frame is a classroom number, not an aesthetic target and not “Navy standard.”

What 13.36% is allowed to mean: on these three male imperial tapes, the published male equation returns about 13.36%. It is allowed to mean you typed 70, 16, and 33 correctly. It is not allowed to mean you are “athletic,” “safe,” “ready to cut,” or free of visceral fat. Pair a tape with waist risk flags used in some guidelines (often discussed around 102 cm / 40 in in men and 88 cm / 35 in in women as crude metabolic screens), blood pressure, and labs if a clinician asked for them. The healthy weight calculator answers a BMI-band question this tape never asks.

Children and teens need pediatric methods, not adult Navy logs. A 60-inch adolescent is not a short sailor. This page does not switch to pediatric coefficients. Older adults lose height; using a remembered peak height instead of today’s standing height changes log10(height) and will not match a clinic stadiometer. Use the height you would write on a medical form today.

Privacy and storage: the key body-fat-calculator-data is unique to this slug. Clearing the form empties fields; it does not wipe other health tools. The split-track class body-fat-split-track is unique so desktop resize does not grab another calculator’s panel. Copy uses the clipboard API via a button; there is no silent exfiltration. Treat any screenshot you share as you would any other health number: it is still not a diagnosis.