How is the API gravity of a liquid bulk product defined?

The API gravity is unique to the oil industry. It is defined via the following equation:

API gravity = [ 141.5 / RD ] – 131.5

RD = relative density of liquid product – see separate FAQ.

Example:

What is the API gravity of the truck load of gasoline with an absolute density of 800 kg/m³ ?

Solution:

• ASTM D1250-80: API = 141.5 / 0.800 791 – 131.5 = 45.20029
• ASTM D1250-04: API = 141.5 / 0.800 788 – 131.5 = 45.20095

(Both values above are rounded to five decimals)

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