How to Measure Body Composition

Plus a Free Body Composition Calculator

Have you ever given up on a diet because your weight stayed the same? Well, what if your weight stayed the same because you lost fat and gained muscle?

That’s what happens when your body composition changes. But you wouldn’t know it from measuring scale weight alone. Therefore, it’s important to measure body composition to see the whole picture.

For that reason, I’m going to share my free body composition calculator. First, let’s talk a little more about body composition.

body composition - hydrostatic weighing

What is Body Composition?

Body composition is a way of describing what your body is made of. For example, your body can be divided into fat and lean mass.

In this case, fat is adipose tissue stored in the body. While lean mass is everything else, including bone and muscle. Generally, your goal is to reduce fat and maintain or increase lean mass. Because that’s what gives you a healthy and attractive physique.

However, the problem is the scale doesn’t tell you anything about how much muscle or fat you have. For that reason, you need a way to measure body composition.

How to Measure Body Composition

You have several options for measuring body composition. And each varies in terms of accuracy and ease of use.

As an example, the main methods for measuring body composition are:

  • Skinfold calipers
  • Bioelectrical impedance
  • Underwater weighing
  • Dexa scanner
  • Bod Pod

Skinfold Calipers

This method uses calipers to measure the thickness of skinfolds at designated sites on your body. Then you put the measurements into a formula in order to calculate your body fat percentage.

Surprisingly, calipers are accurate and repeatable as long as you measure in a consistent manner. However, there is a lot of measurement variation if you’re not careful to do it the same way each time.

For that reason, you should practice first. Then take multiple measures at each site and use the average. Also, it’s a good idea to measure at the same time of day to prevent variation.

Furthermore, calipers are inexpensive and practical for use at home. Click below to get a basic set on Amazon.

Bioelectrical Impedance

Bioelectrical impedance measures your body’s resistance to an electrical signal. The idea is that lean mass contains more water and electrolytes which conduct electrical current. Therefore, you can estimate body composition based on the amount of current that flows through your body.

The biggest benefit of this method is its convenience. In fact, you’ve probably used bathroom scales with sensors built in to measure body fat. In addition, there are handheld versions.

On the other hand, the drawback is that it can be inaccurate. Because it depends on your hydration and electrolyte level.

Although this method isn’t as accurate as calipers, it is very convenient and you can get a nice scale for less than $30.

Underwater Weighing

Also known as hydrostatic weighing. In this method, a person is weighed on dry land and then again underwater.

Underwater weighing is based on Archimedes Principle. Which states the buoyant force on a submerged object is equal to the weight of the fluid displaced by that object. In less nerdy words, your weight underwater is the same as the weight of the water you displace.

Furthermore, water has a known density at room temperature. Therefore, you can calculate your body density. From there, equations determine body fat and lean mass percentages.

Underwater weighing is called the gold standard of body composition tests. However, its accuracy depends on how consistent you can exhale air from your lungs. Along with proper use of the equations.

For this reason, three measurements are performed and the average is taken. I’ve personally used this test (that’s me in the picture below) and got results that seemed very inaccurate despite nearly identical repeat measures. Meaning all the air was expelled from my lungs.

Lastly, it’s also not convenient. Since you need access to a university or company that offers testing to the public.

body composition - hydrostatic weighing

Bod Pod

In principle, the Bod Pod is similar to underwater weighing. Except it uses air displacement instead of water displacement.

The method involves sitting inside a chamber for about 5 minutes. During that time sensors measure your body’s volume. Then equations use your body volume to calculate body fat and lean mass.

Dexa Scanner

Dexa stands for Dual Energy X-ray Absorptiometry. This method uses two types of x-rays to scan the body. And measure the energy absorbed.  Then computer software produces an image and quantifies body composition.


In summary, the easiest and the most practical test is the skinfold caliper method. Although calipers’ accuracy may not be as good as other methods, their precision is very good with practice. Furthermore, you don’t need to know your exact body fat percentage as long as you know if the number is going up or down.

Body Composition Calculator

So you’ve got your skinfold calipers and you’ve learned to take measurements. Now, what do you do with the numbers?  Well, there are a series of complex formulas that convert your skinfold measurements (in millimeters) to body fat percentage.

To simplify the process, I’ve created the body composition calculator. So all you have to do is enter your gender, age, and skinfold measurements. And the calculator does the rest! It even shows you which skinfold sites to measure based on your gender. As well as descriptions of each site in plain English.

body composition - hydrostatic weighing

How to Change Your Body Composition

Now that you know how to measure body composition, how do you change it? Ideally, lose fat and gain muscle.

And Nutritioneering will help with that too! We offer personalized meal plans designed specifically for fat loss and muscle gain.

Check out the Plans page to learn more or click the button below to start customizing your plan right now!

Get Your Custom Meal Plan!

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