Specific Gravity of Water

Why We Can Float in Water

  • Specific gravity is defined as the ratio of the density of a substance to the density of water.
  • Water has a specific gravity of 1.0: any object with a specific gravity less than 1.0 will float in water and anything with a density greater than 1.0 will sink.
  • The human body has a density slightly less than that of water and averages a specific gravity of 0.974, therefore we float.

How Fat and Muscle Affect the Ability to Float

  • Lean body mass, or the mass of the body minus the fat, has a typical density near 1.1, whereas fat mass has a density of about 0.9. Therefore, an individual who has a high percentage of lean body mass may require floatation devices.
  • In contrast, an obese individual will have a specific gravity considerably less than 1.0 and will float more easily.