Body Composition

How to Accurately Measure Body Composition

Matthew Mace
February 2, 2023

How Do DEXA, Underwater Weighing, Bod Pod, Smart Scales, and Calipers compare to Spren Body Composition Imaging?

Spoiler alert: the only truly accurate method of measuring body fat is to do it post-mortem. All body fat analysis methods, even DEXA, which is often considered the “gold standard” approach [7], calculate various metrics and plug these into standard equations to determine body composition results.

So, all accessible body composition analysis methods will never be 100% accurate—it’s just not possible. However, some methods are more accurate than others and provide further insights.

In this article, we explain how to measure body composition using the most common methods. We’ll highlight the pros and cons of each method, how they work, and more. But first, a quick definition of body composition.

What is body composition? 

Body composition provides us with a more accurate picture of precisely what our bodies are made up of.

This has very quickly become an important—and preferred method—of determining the desirable body weight of healthy adults and athletes [4].

For example, unlike traditional weight measurement tools, such as a set of scales or standard BMI equations, body composition tells us percentages of fat, muscle, and bone in the body.

These insights allow us to go beyond the scale, assessing how healthy an individual actually is.

How to measure body composition

In total, there are six main body composition analysis methods, including Spren. These are as follows:

  1. Dexa Scan
  2. Skinfold Test
  3. Underwater Weighing
  4. Bod Pod
  5. BIA Scale
  6. Spren

We’ve provided you with an accuracy comparison table below—it includes key measurements for each method, alongside the average cost of a scan.

Dexa Scan

How it works: A Dexa Scan, also known as dual-energy x-ray absorptiometry, uses x-rays to calculate the distribution of lean muscle mass, fat mass, bone, and water in the body. During the scan, two x-ray beams—of which are very safe—pass through bodily tissues. The varying energy absorption allows practitioners to measure body composition, including fat distribution, accurately. 

And as already mentioned, it’s often considered the “gold standard” body composition analysis tool, adopted by many healthcare professionals and commonly used in a clinical setting [8].


  • Measures bone density: no other method calculates bone density—this is ideal for revealing osteoporosis and other bone-related conditions and perhaps even risk factors.
  • Very accurate analysis method: one of the best methods for accurate body composition results, also showing fat distribution. 


  • Can be very expensive: scans can cost upwards of $150.
  • You are exposed to radiation: although only small doses, some people can be sensitive to the exposure. You will experience a similar amount of radiation to a short flight.
  • Not convenient: most people are unlikely to book regular Dexa Scans.

Skinfold Test

How it works: A pair of skinfold calipers are used to measure the thickness (mm) of the skin at various sites on the body, including the abdominal, thighs, triceps, and chest). 

The skinfold test has been around for decades, and although it’s relatively easy to do, results can be inaccurate and present several downsides. For example, the test relies on two predictions to provide results, reducing validity [10].

We cover more of the downsides, alongside a few benefits below.


  • Widely used method: commonly used to accurately measure fat distribution. 
  • Good for measuring weight changes in children: skinfolds have limited utility for overweight and severely obese adults [2].


  • Invasive: some people may find the skinfold test invasive and uncomfortable.
  • Uses two predictions to calculate results: this creates room for error and may produce inconsistent and unreliable results.
  • Must be done by a professional: lots of room for error (e.g., measuring the wrong site), so it must be done by a professional for accurate results. 

Underwater Weighing 

How it works: The participant sits down on a scale while submerged in a tank of water. It’s important to exhale fully to reduce error and ensure accurate results. The test is usually repeated three times for reliability. 

Underwater weighing relies on the Archimedes principle—which states that when your body is completely submerged, the volume of fluid displaced is equal to the volume of the body [5].

You are also weighed before completing the test. Test administrators use these measurements to calculate body fat percentage. Moreover, because muscle tissue is denser than fat tissue, if your underwater weight is heavy, this indicates a lower body fat percentage.

According to research, underwater weighing is one of, if not the most valid technique for assessment of body fat and lean tissue in a clinical setting—aside from post-mortem analysis [3]. But it does have a few downsides. For example, underwater weighing is uncomfortable, not convenient, and does not measure two key metrics: fat distribution and bone density. 


  • Accurately measures body volume: the Archimedes principle is an accurate method of analysis. 


  • You must be submerged underwater: many people find this uncomfortable or even terrifying.
  • Must be done in a laboratory with a trained specialist: this is not a convenient or accessible option, often leading to irregular check-ins.
  • Sources of error: if the participant does not exhale fully during the test, the body fat readings will be inaccurate. 

Bod Pod

How it works: the participant enters an enclosed pod where body volume is measured via air displacement plethysmography. This accurately calculates body density.

The Bod Pod has become more popular in recent years, but the results are not as extensive or impressive compared to other methods, such as underwater weighing and Dexa Scans [9].


  • Accurately measures body volume: air displacement accurately measures body volume.


  • Bad for claustrophobic people: confined spaces make this a poor option for those who do not like small or tight spaces.
  • Expensive to purchase the equipment: it costs upwards of $50,000 to purchase a Bod Pod.

BIA Scale

How it works: small electrical currents are sent through the body to measure body composition. All bodily tissues, including muscle and fat, differ in electrical conductivity—this is because the water content varies.

BIA, known as bioimpedance analysis, is non-invasive, low cost, and is currently one of the more popular body composition analysis methods that you can do yourself at home [6]. Although, it does have its limitations—more on these below.


  • Non-invasive: can be done at home, with no professional help.
  • Easy to do and highly repeatable: you can perform routine scans for accurate body composition analysis over a set period.


  • Not the most accurate method for severely obese people: assumes the hydration factor of the fat-free mass is constant and is not different in the obese population. Also, body geometry and water distribution are likely to differ [1].
  • Inadequate hydration may report incorrect results: fat-free mass and bone density may be underestimated if dehydrated. 
  • Does not measure fat distribution: BIA measures total fat but cannot report accurate fat distribution (e.g., android and gynoid fat). 

Measuring tape

We have a bonus method for you—one that you can do at home—but it does not provide the most accurate results. The measuring tape method is best paired with another measurement for increased reliability.

That’s right: you can use a tape measure and a handy equation to calculate an estimated body fat percentage. 

How it works: take measurements around your hips, waist, and neck. An equation is used to estimate total body volume and subsequent body fat percentage.


  • Low cost: the most cost-effective body composition method, but the results are the least accurate and may contain human error.
  • Highly convenient: you can do this yourself from the comfort of your own home in privacy. 


  • Some people may find this method stressful: you may be unsure where to measure on the body for accurate and repeatable results.


How it works: Spren uses your smartphone camera, machine learning algorithms, and computer vision to provide you with accurate and reliable body composition analysis results.

It’s as simple as snapping a pic, waiting for your results, and tracking your progress.

Spren automatically generates numerous key biomarkers to help you monitor your health, going beyond the scale and showing you an accurate body composition analysis. 


  • Easy to do: snap a full-body selfie and let Spren go to work.
  • Laboratory accuracy from the comfort of your home: gain valuable insights without invasive testing procedures.
  • View fat distribution: measure fat distribution to reach your long-term goals.


  • Does not measure bone density: Dexa Scans are typically the best option for bone density analysis.

Why is body composition important?

Now that you know what body composition is and how to measure it, you might be wondering: why does it actually matter?

Routinely measuring your body composition enables you to monitor your health and accurately progress toward your deeper health goals. For example, you can track marginal changes in fat and lean mass that would be very difficult to notice visually.

This data allows you to remain confident that you’re making progress, making it that much easier to stick to your nutrition and exercise plan.

Similarly, a body composition analysis tool that reveals fat distribution allows you to check risk factors for certain diseases and health conditions. For example, people with a higher android fat percentage—fat found in the abdomen, chest, and back of the neck—are more at risk of severe acute pancreatitis [7].

Fat distribution analysis enables you to take action to avoid various health conditions related to weight distribution, including stroke, type 2 diabetes, high blood pressure, hypertriglyceridemia, and impaired glucose tolerance. 

How do you improve your body composition?

So, the big question: how do you improve your body composition? 

The best way to improve your body composition is to measure your body composition regularly using an accurate and repeatable method, such as Spren. 

Doing so allows you to see changes in your body, including muscle and fat distribution. You can then adopt or change lifestyle and health habits in pursuit of your long-term goals, whether that means losing weight to reduce your risk of type 2 diabetes, or simply gaining muscle mass and limiting fat gain.

Use Spren today for an accurate, reliable, and easy body composition analysis, all done from your smartphone camera.


  1. Deurenberg, P., 1996. Limitations of the bioelectrical impedance method for the assessment of body fat in severe obesity. The American journal of clinical nutrition, 64(3), pp.449S-452S.
  1. Duren, D.L., Sherwood, R.J., Czerwinski, S.A., Lee, M., Choh, A.C., Siervogel, R.M. and Chumlea, W.C., 2008. Body composition methods: comparisons and interpretation. Journal of diabetes science and technology, 2(6), pp.1139-1146.
  1. Francis, K.T., 1990. Body-composition assessment using underwater weighing techniques. Physical Therapy, 70(10), pp.657-662.
  1. Jackson, A.S. and Pollock, M.L., 1985. Practical assessment of body composition. The Physician and sportsmedicine, 13(5), pp.76-90.
  1. Katch, F.L.E.D.M., Michael, E.D. and Horvath, S.M., 1967. Estimation of body volume by underwater weighing: description of a simple method. Journal of Applied Physiology, 23(5), pp.811-813.
  1. Khalil, S.F., Mohktar, M.S. and Ibrahim, F., 2014. The theory and fundamentals of bioimpedance analysis in clinical status monitoring and diagnosis of diseases. Sensors, 14(6), pp.10895-10928.
  1. Mery, C.M., Rubio, V., Duarte-Rojo, A., Suazo-Barahona, J., Peláez-Luna, M., Milke, P. and Robles-Díaz, G., 2002. Android fat distribution as predictor of severity in acute pancreatitis. Pancreatology, 2(6), pp.543-549.
  1. Shepherd, J.A., Ng, B.K., Sommer, M.J. and Heymsfield, S.B., 2017. Body composition by DXA. Bone, 104, pp.101-105.
  1. Wagner, D.R. and Heyward, V.H., 1999. Techniques of body composition assessment: a review of laboratory and field methods. Research quarterly for exercise and sport, 70(2), pp.135-149.
  1.  Wells, J.C. and Fewtrell, M.S., 2006. Measuring body composition. Archives of disease in childhood, 91(7), pp.612-617.

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Matthew Mace

Matthew is a keen cyclist and freelance health and wellness content writer. He studied sport and exercise at Durham University and now writes for numerous active brands. When he's not writing or cycling, he can be found on the edge of his seat watching the Formula One.

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