While the question asks about fat density, it is more common and practical to discuss and calculate body density to assess body fat composition. Therefore, this answer will address how to calculate body density, which is a key step in determining body fat percentage. Body density is calculated using a person's body mass and volume.
Calculating Body Density
The most common method mentioned for calculating body density is hydrodensitometry, also known as underwater weighing. According to reference information on hydrodensitometry, you calculate body density by dividing body weight (mass) by body volume.
Here's the formula:
Body Density = Body Weight (Mass) / Body Volume
Steps Involved in Hydrodensitometry:
-
Measure Body Weight (Mass): This is typically measured in kilograms (kg).
-
Measure Body Volume: This is determined by underwater weighing. The individual is submerged in water, and their weight underwater is recorded. Adjustments are made for residual lung volume and air in the gastrointestinal tract.
-
Calculate Body Density: Use the formula above: Body Weight / Body Volume.
Example
Let's say a person weighs 70 kg and their body volume, as determined by underwater weighing, is 0.068 cubic meters.
Body Density = 70 kg / 0.068 m3 = 1029.41 kg/m3
This density value can then be used in equations (like the Siri equation) to estimate body fat percentage. Note that the density of pure fat is roughly 0.9 g/cm3 (or 900 kg/m3), and the density of lean tissue is roughly 1.1 g/cm3 (or 1100 kg/m3). The overall body density falls somewhere in between, depending on the proportion of fat and lean tissue.
