How the military measures body composition

The DoD Instruction about physical fitness and body composition requirements for Service Members was updated in 2022, and DoDI 1308.03 outlines the latest rules. All Service Members are still required to have a body composition assessment at least once per year—and expected to meet these standards to maintain operational readiness, successfully perform their duties, and reduce the risk for injuries and obesity-related diseases.

Body composition basics

Body composition can be estimated in many different ways, each with its own pros and cons. The only ways to measure the exact amounts of body fat and the various types of lean body mass are direct measurement after death or advanced imaging. Advanced imaging is expensive and time-consuming, so it’s rarely used for body-fat assessments outside of research settings.

Practical body-composition assessments simply need be valid and reliable, which means they measure what they’re intended to measure with reasonable accuracy and their measurements are consistent. For military use, measurement methods also need to be easy to learn without special expertise, since most Service Members doing the assessments aren’t medical providers or fitness experts.

The DoDI sets the standard but allows each Service to choose which method they use to measure body composition. DoDI 1308.03 states: “Body composition may be evaluated using either BF (body fat) calculations, waist-to-height ratio, abdominal circumference, height-weight screening, or any combination thereof.”

Body mass index

The weight standards used by the military, as set by DoDI 1308.03, are a close approximation of BMI. Body mass index (BMI) is a tool to quickly categorize someone as underweight, healthy weight, overweight, or obese, based on their height and weight. BMI is an accepted and reliable way to assess body composition. With a scale, a way to measure height, and CDC’s adult BMI calculator, it’s hard to get a BMI calculation wrong.

But using BMI has some limitations. The main limitation is that it doesn’t account for differences in body composition. For different people with the same BMI, their percentage of body fat (BF%) can vary based on sex, race, age, and physical fitness level. So having an “overweight” BMI doesn’t necessarily mean you’re unhealthy. For example, BMI tends to classify short, muscular people as overweight. If you take more measurements, such as abdominal circumference, you’ll find those people aren’t “overfat,” so they might not have the health risks their BMI suggests.

BMI is a fairly accurate measure of body fat for values over 30. It’s unlikely someone with an “obese” BMI of 30 or more is misclassified because they’re very muscular with little body fat. Those few people where that’s the case are usually high-level athletes who don’t carry excess body fat. People who have high levels of both lean body mass and fat are still likely to be considered obese and have the risks that come with carrying excess body fat.

Even with its limitations, the science supporting the use of BMI as a risk screen holds strong. People who are overweight or obese are at greater risk for various preventable chronic diseases, such as heart disease and cancer. BMI is a quick-and-easy screening tool to identify people who might benefit from health-behavior improvements. But BMI shouldn’t be used as a “go, no-go” type of measure for whether you’re healthy or not. If you screen outside the “normal” category, it simply means you should take a closer look at body composition and lifestyle factors that might increase your risk for illness.

Military weight standards

DoDI 1308.03 states that, when using height-weight screening, the maximum allowable weights must be between a BMI of 25 and 27.5, and the minimum allowable weights can’t be lower than a BMI of 19. Each Service is allowed to set their specific weight standards, as long as the maximums and minimums are within those BMI ranges. This allows men and women to carry a healthy amount of fat mass, which is necessary for both health and performance. It also accounts for people who are very muscular for their height.

Similar to BMI, the purpose of military weight-for-height measurement is as a rapid screen for excess body fat. If you screen outside the allowable range, more measurements (which vary depending on Service branch) will be taken to find out whether you have an unhealthy amount of body fat or if you’re just muscular.

Body-circumference measurement

DoDI 1308.03 also establishes the acceptable methods for assessing body composition and determining body fat. The Services usually screen a member’s weight first, and then estimate body fat only if a member doesn’t meet the weight-for-height standards. Prior to March 2022, the only method allowed was 2- and 3-site body-circumference measurements (also called the “tape test”), unless an exemption was granted. For this method, a “self-tensioning tape measure” is used to measure body circumference—at the neck and navel for males, and at the neck, narrowest portion of the waist, and hips for females. The updated DoDI now allows other methods, in addition to 2- and 3-site taping, to measure body fat.

Here are the tests each Service now uses.

  • The Department of the Air Force (DAF) started using the waist-to-height ratio method to assess body composition in January 2023. Waist-to-height ratio (WHtR) is calculated as waist circumference—measured at the midpoint between the iliac crest (top of the hip bone) and the lowest rib—divided by height. WHtR is well-established as a screening tool for risk factors such as high blood pressure, diabetes, and metabolic syndrome, and it’s considered better than measuring waist circumference and BMI in predicting risk factors.

    Generally, the goal WHtR is 0.5 or lower—meaning your waist circumference is less than half of your height. The DAF standards, as outlined in the Air Force and Space Force memoranda in January 2023, set the WHtR standard at 0.55. Above this, Airmen and Guardians are considered to be out of standards.
  • The Army and the Marine Corps use 2- and 3-site circumference measurements, each using slightly different formulas to create the body fat tables in their body composition programs. Despite the formula differences, the results are within about 1% of each other.
  • The Navy uses a single-site abdominal-circumference measurement. If a Sailor doesn’t meet abdominal circumference standards, then the 2- or 3-site measurements will be measured for a final BF%.
  • The Coast Guard first assesses weight-for-height. If a Coastie is out of weight standards, BF% is then measured using 2- or 3-site circumference measurements. Finally, if someone still doesn’t meet standards, single-site abdominal circumference is measured.

One of the main reasons the military uses circumference measurement as the standard for assessing body composition is because it’s easy to learn for the Service Members doing the assessments. Other, similar measurements, such as skinfold measurements, are also cost-effective, valid, and reliable, but they take longer to learn and require raters to be more highly skilled, which affects the reliability of newly trained raters. Despite some Service Members believing otherwise, body-circumference measurements—whether 2- and 3-site, abdominal circumference, or WHtR—are valid, reliable, and extremely cost-effective.

There is some controversy about using circumference measurements, particularly for women because they carry more fat in their hips and thighs compared to men. Waist and hip measurement standards are based on typical female fat distributions and take into account women who have more “pear” or “hourglass” shapes with narrower waists, as well as “apple” shapes with bigger waists. The controversy is that measuring around the widest part of the hips includes the gluteus (butt and hip) muscles, and strength-and-conditioning programs often train the glutes for muscle hypertrophy. As a result, bigger glute muscles can lead to overestimating total body fat.

To ensure 2- and 3-site body-circumference measurements are both accurate and fair, the Marine Corps studied—and found—that current methods and calculation formulas are still accurate, and resulted in overestimating BF% only slightly. The measurements correctly classified 91.5% of male Marines and 92% of female Marines. The tape tests misclassified 0.6% of men and 6.3% women by overestimating BF%, and misclassified 7.9% of men and 1.6% women by underestimating BF%—compared to dual-energy X-ray absorptiometry (DEXA or DXA) measurement. As a result of the study, Marines who are over BF% standards will now have confirmation measurements done using DXA or bioelectrical impedance analysis (BIA) before negative administrative action (such as placement in the body composition program) is taken. More information about the Marine Corps updates can be found at MARADMIN 423/22. (Results of a similar Army study were still pending when this article was published.)

Other (unapproved) methods of measurement

Skinfold measurement is similar to circumference measurement in terms of validity and reliability, but it requires experienced raters. It takes close to 120 practice tests for a rater to become proficient, creating a time burden to effectively train and maintain the capability of raters. Measuring skinfold also has inconsistencies related to age, making it complicated for general use. While measuring skinfold can be an excellent tool for trained medical and physical fitness professionals who do it often, it’s less practical for overall use by military personnel.

Bioelectrical impedance analysis (BIA) calculates body composition based on how quickly a (harmless) electrical current passes through your body—because bone, muscle, and fat have different electrical-resistance properties. But the validity of BIA is affected by conditions such as hydration levels and waist circumference. Overhydration can lead to lower readings, making it fairly easy to “cheat” a BIA test. BIA devices also vary in reliability, and those that perform more accurately and consistently are generally more expensive.

Air-displacement plethysmography (ADP, commonly known by the brand name BOD POD) calculates body composition by measuring air-pressure differences between a chamber where the test subject is sitting and an empty control chamber. ADP is reliable, but its validity can be hit or miss, and it sometimes underestimates BF%. ADP is becoming more widely available in Army Wellness Centers and Air Force Health and Wellness Centers. It can be useful to track your BF% throughout the year if you’re trying to shed some body fat. But ADP needs more rigorous testing to validate its use in military populations, and the equipment is extremely expensive.

Dual-energy X-ray absorptiometry, also called DEXA or DXA, is one of the most accurate measures of body composition. But it’s neither time- nor cost-effective outside of medical or research settings. A single test can take about 15 minutes, and machines cost tens of thousands of dollars, making it difficult to fund even a single machine.

Bottom line

DoD and the Service branches took many considerations into account when choosing methods for assessing body composition, including whether a measurement type is valid, reliable, time- and cost-effective, and how easily a Service Member can take the measurements. Whatever method is used, the purpose of the DoDI standards and Service-specific tests is to ensure the health and readiness of every Service Member, and to reduce the risk of injuries and chronic disease.

Additional resources

For more information about U.S. military body-composition standards, here are the regulations:

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