The formula to calculate API gravity from specific gravity (SG) is:
$${\displaystyle {\text{API gravity}}={\frac {141.5}{\text{SG}}}-131.5}$$
Conversely, the specific gravity of petroleum liquids … See more

To derive the API gravity, the specific gravity (i.e., density relative to water) is first measured using either the hydrometer, detailed in ASTM D1298 or with the oscillating U-tube method … See more

Generally speaking, oil with an API gravity between 40 and 45° commands the highest prices. Above 45°, the molecular chains become shorter and less valuable to refineries. See more

In the oil industry, quantities of crude oil are often measured in metric tons. One can calculate the approximate number of barrels per … See more

There are advantages to field testing and on-board conversion of measured volumes to volume correction. This method is detailed in ASTM D287.
The hydrometer method is a standard technique for directly measuring API gravity of petroleum … See more

• Comments on API gravity adjustment scale
• Instructions for using a glass hydrometer measured in API gravity See more