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If an oil has 26.5 deg of API, then its specific gravity is calculated as
s = 141.5 / ( 131.5 + 26.5 )
s = 0.8956

The American Petroleum Institute gravity, or API gravity , is a measure of how heavy or light a petroleum liquid is compared to water: if its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks.

API gravity is thus an inverse measure of a petroleum liquid's density relative to that of water (also known as specific gravity ). It is used to compare densities of petroleum liquids . For example, if one petroleum liquid is less dense than another, it has a greater API gravity. Although API gravity is mathematically a dimensionless quantity (see the formula below), it is referred to as being in 'degrees'. API gravity is graduated in degrees on a hydrometer instrument. API gravity values of most petroleum liquids fall between 10 and 70 degrees.

Thus, a heavy oil with a specific gravity of 1.0 (i.e., with the same density as pure water at 60 °F) has an API gravity of:

The specific gravities of gases usually are compared to dry air which generally has a density of 1.29 g per litre. The specific gravity of all other materials is compared to water as a fraction heavier lighter or heavier density.

Where SG = specific gravity, ρ = density of the material (kg/m 3 ), ρW = density of water ( kg/m 3 ). The reference density of water at 4 o C (39 o F) is used as the reference as these are the conditions of maximum density.

There is a wide range of instruments designed to measure the specific gravity of a material. The hydrometer can be used to measure the specific gravity of any liquid. The device is designed to float freely at the liquid surface with a protruding stem giving a reading corresponding to the specific gravity of the liquid. Other instruments to measure specific gravity are the Pycnometer, and digital density meters based on oscillating U-tubes.

If an oil has 26.5 deg of API, then its specific gravity is calculated as
s = 141.5 / ( 131.5 + 26.5 )
s = 0.8956

The American Petroleum Institute gravity, or API gravity , is a measure of how heavy or light a petroleum liquid is compared to water: if its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks.

API gravity is thus an inverse measure of a petroleum liquid's density relative to that of water (also known as specific gravity ). It is used to compare densities of petroleum liquids . For example, if one petroleum liquid is less dense than another, it has a greater API gravity. Although API gravity is mathematically a dimensionless quantity (see the formula below), it is referred to as being in 'degrees'. API gravity is graduated in degrees on a hydrometer instrument. API gravity values of most petroleum liquids fall between 10 and 70 degrees.

Thus, a heavy oil with a specific gravity of 1.0 (i.e., with the same density as pure water at 60 °F) has an API gravity of:

If an oil has 26.5 deg of API, then its specific gravity is calculated as
s = 141.5 / ( 131.5 + 26.5 )
s = 0.8956


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