Specific Gravity Unit

Definition - What does Specific Gravity Unit mean?

Specific Gravity Unit, also known as specific gravity is the density of a unit object divided by the density of a reference substance. In usual cases, the reference substance used is water, which is considered to have a density of 1 gm/ml or 1 gram per cubic cm. The specific gravity unit of any substance is a dimensionless quantity and has no units.

Petropedia explains Specific Gravity Unit

In oil and gas context, specific gravity is inversely proportional to API gravity. In order to find out the specific gravity of crude oil and petroleum liquids, this formula can be used:

Specific Gravity at 60 Degree F = (141.5) / (API Gravity + 131.5)

Using this formula, we can derive the API gravity of crude oil. For example, heavy crude oil has a specific gravity of 1.0 and will have its API gravity as follows:

API Gravity = (141.5 / 1.0) – 131.5 = 10.0 degree API

API gravity is considered to be one of the important factors in deriving the price of a crude oil. It also lets us know whether the crude oil is a light or heavy.

The API values for various classification categories of crude oil are as follows:

  • Light – API > 31.1
  • Medium – API between 22.3 and 31.1
  • Heavy – API < 22.3
  • Extra Heavy – API < 10.0
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