Everything You Need To Know

About Hydrostatic Body Fat Testing

What is a Hydrostatic Body Fat Test?

Underwater weighing is based upon Archimedes Principle which states that the buoyant force on a submerged object is equal to the weight of the fluid that is displaced by the object. We can use this principle to determine a person's percentage of body fat because the density of fat mass and fat-free mass are constant.

Definition:  Hydrostatic weighing, also referred to as "underwater weighing," "hydrostatic body composition analysis," and "hydrodensitometry," is a technique for measuring the mass per unit volume of a living person's body. It is a direct application of Archimedes' principle, that an object displaces its own volume of water.

Lean tissue, such as bone and muscle, are more dense than water, and fat tissue is less dense than water. Basically, muscle sinks and fat floats. Therefore, a person with more body fat will weigh less underwater and be more buoyant. Someone with more muscle will weigh more underwater.

Why should I try Hydrostatic Weighing?

Body fat testing (rather than just stepping on your simple home scales) is the best way to find out what you are really made of!  Research shows that Hydrostatic Testing (Underwater Weighing) has become universally regarded, by industry experts, as the "Gold Standard" in body fat testing.

Whether you are looking to lose weight, gain weight, or just maintain your current weight, having a Hydrostatic Body Fat Test done will provide you with a wealth of information to let you know how you're doing.

"That hydrostatic testing (underwater immersion) is the most accurate method for body fat determination." Renowned author and fitness expert Covert Bailey, in the phenomenal best seller "Fit or Fat"

We obtain your dry weight and wet weight (based on buoyancy) and are able to scientifically calculate your body fat as a percentage of your total weight. Your scales at home cannot tell you if your weight loss/gain is muscle or fat.  However, a Hydrostatic Body Fat Test can tell you, to the ounce, what took place with your body during your weight loss/gain regiment.

How do other body fat testing methods compare?

Hydrostatic Body Fat Test

According to research, “Hydrostatic Body Fat Testing” is still the “Gold Standard” to which all methods of body fat testing still compare themselves. However, for informational purposes we would like to share other methods that are being used within the health, fitness, and medical community.


  • Regarded as the “Gold Standard” in body fat testing
  • Fast test time (5-10 minutes)
  • Most accurate technology available today
  • Provides the best repeatability from test to test (tracking changes)
  • Error rate around 1.5%
  • Low equipment maintenance
  • Has been the most accurate method for over 30 years


  • Requires knowledge to administer test
  • Being submerged underwater might be a little difficult for some (if you’re uncomfortable going underwater for a few seconds.)
  • Must be able to blow out your air

Duel Energy X-Ray (Dexa)

DEXA uses two x-ray energies to measure body fat, body fat percentage, muscle and bone mineral. One must lie down on an x-ray table while the machine scans the body. It takes the machine about 10 to 15 minutes to produce the image of the tissue.


  • Under proper conditions it provides accurate results
  • Error Rate is less than 2% under proper conditions
  • Radiation exposure is relatively low but it is still new technology


  • Very expensive equipment
  • High Cost per test
  • Different DEXA equipment can produce different results
  • X-Ray license required to use machine
  • Frequent testing may be of concern due to radiation exposure
  • Was designed for discriminating bone density as opposed to soft tissue such as organs, muscle and fat

Caliper Body Fat Test

This is a small pinching device that measures subcutaneous body fat on your body. It has a +/- 3-8 percent error ratio based on technician skill, quality of caliper used, and number of sites pinched. Although it’s quick and relatively easy to get it’s more of an estimate of body fat this is because it only measures a few areas on your body and not the whole thing. Plus, it is very subjective to each person that does the testing.


  • Easy to use once skill is mastered
  • Does not require much time
  • Noninvasive method
  • Inexpensive way of estimating body fat percent
  • Portable


  • Technical sources of error
  • Error rate up to +/-8%
  • Mostly concerned with subcutaneous fat (under the skin)
  • May not be an ideal measurement for those who are obese, or very lean.
  • Reliability is highly dependent upon skill and the type of calipers used

Bod Pod Body Fat Testing

This method tries to compare itself to the Hydrostatic method of body fat testing and it is based on similar principles. However, instead of using water it uses air displacement instead. This method has conflicting research reported on its results. Humidity, temperature, body hair and other environmental issues have been reported to negate the results of its body fat readings. According to Georgia State University, if each body fat test is performed correctly to the recommended guidelines, there is a +/-3% error.


  • Fast 5 -10 minutes
  • Not difficult to operate


  • Error ratio +/-3 percent
  • Results effected by body temp of muscles
  • Hydration levels can effect results
  • Body hair can have an effect on the results
  • Very expensive equipment
  • Breathing pattern might affect the results
  • Can have a claustrophobic effect


Find out exactly what you're made of.


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