API Gravity Calculator


About API Gravity Calculator (Formula)

API gravity is a measure of the density of liquid petroleum products in comparison to water. It’s used as an indicator of the quality of crude oil and other petroleum products. The API gravity scale is defined so that higher values indicate lighter or less dense liquids, while lower values indicate heavier or denser liquids. The API gravity calculation involves a simple formula that allows you to convert specific gravity (SG) measurements to API gravity.

The formula to calculate API gravity is:

API Gravity=141.5Specific Gravity at 60°F/60°F−131.5


  • 141.5 is a constant used to align the API gravity scale with the specific gravity scale at a reference temperature.
  • 131.5 is a constant that serves to adjust the scale to make water have an API gravity of 10.

In this formula, the specific gravity (SG) of the liquid is measured at a temperature of 60°F (15.6°C) and is compared to the density of water at the same temperature.

Here’s how the calculation works:

  1. Measure the specific gravity of the liquid at 60°F/15.6°C using a hydrometer or other appropriate measuring instrument.
  2. Plug the specific gravity value into the formula: API Gravity=141.5Specific Gravity at 60°F/60°F−131.5
  3. Perform the arithmetic operations to calculate the API gravity value.

The resulting API gravity value provides valuable information about the quality of crude oil and other petroleum products. Lighter crude oils, which have higher API gravity values, are typically easier to refine into high-value products like gasoline. Conversely, heavier crude oils with lower API gravity values require more extensive refining processes to yield useful products.

API gravity is an essential parameter in the oil and gas industry, influencing decisions related to production, refining, transportation, and pricing of petroleum products. It’s also commonly used in regulatory contexts and international trade agreements to classify and value different types of crude oil.

Keep in mind that this API gravity formula assumes measurements are made at the specified temperature conditions (60°F/15.6°C) and that the liquid being measured is a petroleum product. Other formulas may be required for different temperature scales or non-petroleum liquids.

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