API Gravity Calculator

The API gravity calculator estimates the API gravity of petroleum liquids. API gravity is extensively used as a measure of the grade of crude oil products. The API gravity is a function of the relative density or specific gravity of the crude oil liquid. This calculator will help you answer questions like, what is the API gravity of gasoline or petrol? Read on to understand more on the specific gravity to API conversion formula.

The API gravity is a measure of the heaviness of crude oil products when compared with water. The term API in API gravity stands for American Petroleum Institute, with reference to the institution that developed it. The API gravity is calculated based on the specific gravity of the liquid. To find the API gravity of a liquid, initially, the relative density is calculated using a hydrometer or an oscillating U-tube conforming to industry standards ASTM D1298 or D4052. The specific gravity is then used in the API gravity formula. The API gravity of a crude product is related to the specific gravity using the equation:

Specific Gravity = 141.5 / (131.5 + API)

Rearranging the terms, we get:

API = (141.5 / Specific Gravity) - 131.5

The above equation can also be called the specific gravity to the API conversion formula. The API gravity parameter is dimensionless, based on the equation. However, it is often used with a degree symbol, such as the degree of API gravity (° API). The specific gravity of the liquid can be estimated from its density the same way as in our specific gravity calculator using the equation below:

Specific gravity = ρ_Liquid / ρ_water,

where the density of water is taken as 999 kg/m³. Therefore, one can directly calculate API gravity from density.

The API gravity is often compared with water such that, the relative density of heavy oil at 60°F is taken as 1.0, the same value as for pure water.
The API gravity for pure water in that case will be:
API = (141.5 / 1) - 131.5 = 10° API

The behavior of the crude products in water is judged based on this parameter. If the API gravity of a liquid is greater than 10° API, the liquid will float on water. However, if the value of API gravity is less than 10, it implies that the liquid is heavier than water and will sink.

To determine the API gravity of a petroleum liquid:

1. Enter the density of the liquid.
2. The calculator will determine the relative density of the liquid.
3. The API gravity calculator will calculate the API gravity from density.

Note: You can also directly choose liquid from the pre-existing list of alternatives, available in the Advanced mode of the calculator.

Question: What is the API gravity of gasoline? Take the density of gasoline as 750 kg/m³.

To determine the API gravity of gasoline:

1. Enter the density of the gasoline as 750 kg/m³.
2. You can now see the relative density of the gasoline as 0.7508.
3. Using the API to specific gravity conversion calculator:
   API = (141.5 / 0.7508) - 131.5 = 56.98° API.

The API gravity can be related to its value such that the high API are lighter crude oil products and are more valuable as they can yield more high-value products when processed. However, crude products having API values beyond 45° are less valuable as they are considered extra light. The degree of API for most crude products is between 15-45° with 35-45° being most valuable.