API Gravity
Calculate API gravity from density or product using API = 141.5/SG − 131.5. Free petroleum gravity calculator with oil classification and interactive charts.
About This Calculator
The API Gravity Calculator determines the API gravity of petroleum liquids — a critical measure of crude oil quality used throughout the oil and gas industry. Developed by the American Petroleum Institute (API), this scale tells you how heavy or light a petroleum liquid is compared to water. Enter the density in kg/m³ or select a common crude product to instantly compute the API gravity, specific gravity, and oil classification.
API gravity is calculated using the formula: API = (141.5 / SG) − 131.5, where SG (specific gravity) = density of liquid / density of water at 60°F (999 kg/m³). Liquids with API gravity greater than 10° float on water, while those below 10° sink. The scale ranges from extra heavy crudes below 15°API to extra light crudes above 45°API. Light crude oils (35–45°API) are the most valuable because they yield more high-value products like gasoline, diesel, and jet fuel during refining.
This calculator includes a built-in product selector with common petroleum liquids including gasoline (~750 kg/m³, ~57°API), kerosene (~775 kg/m³, ~51°API), diesel grades 1D through 4D, fuel oils, and light/medium/heavy crude oils. The API gravity scale is standardized by ASTM D287 and ASTM D1298 and is widely used for crude oil trading, refinery optimization, and marine fuel classification.
API Gravity Classification Guide
Crude oils are classified by API gravity for trading and refining purposes. Extra Heavy crudes (<15°API) include bitumen and oil sands requiring specialized extraction. Heavy crudes (15–25°API) need more refining but are increasingly produced globally. Medium crudes (25–35°API) are the most common benchmark grades. Light crudes (35–45°API) like West Texas Intermediate (WTI, ~39.6°API) and Brent (38.1°API) are premium grades used as pricing benchmarks worldwide. Extra Light crudes (>45°API) like condensates are valuable but require special handling.
Frequently Asked Questions
What is API gravity?
API gravity is a measure of how heavy or light a petroleum liquid is compared to water. Developed by the American Petroleum Institute (API), it is calculated using the formula API = (141.5 / Specific Gravity) - 131.5. Higher API gravity indicates lighter crude oil.
How is API gravity calculated?
API gravity is calculated by first finding the specific gravity (density of liquid divided by density of water at 60°F, which is 999 kg/m³) and then applying the formula: API = (141.5 / Specific Gravity) - 131.5. Simply enter the density in kg/m³ or select a common petroleum product.
What does API gravity indicate about crude oil?
API gravity classifies crude oil into categories: Extra Heavy (<15°API), Heavy (15–25°API), Medium (25–35°API), Light (35–45°API), and Extra Light (>45°API). Light crude oils with higher API gravity are generally more valuable as they yield more high-value products like gasoline when refined.
What is the API gravity of water?
Pure water has an API gravity of 10° at 60°F. This is because the specific gravity of water relative to itself is 1.0, and plugging this into the formula gives: API = (141.5 / 1.0) - 131.5 = 10° API. Liquids with API gravity above 10° float on water, while those below 10° sink.
What is the API gravity of gasoline?
Gasoline has an API gravity of approximately 56.98° API, based on a typical density of 750 kg/m³. This high API gravity makes gasoline lighter than water and most other petroleum products. Gasoline falls in the Extra Light category and floats on water.
What is the API gravity of diesel?
Diesel fuel typically has an API gravity ranging from 30 to 42° API depending on the grade. Diesel 1D has about 37.3°API (density ~830 kg/m³), Diesel 2D has about 34.7°API (density ~850 kg/m³), and Diesel 4D has about 22.2°API (density ~920 kg/m³).
How does temperature affect API gravity?
API gravity is measured at a standard reference temperature of 60°F (15.56°C). Since liquids expand when heated, the density and therefore API gravity changes with temperature. The API standard ASTM D1250 provides correction tables to adjust API gravity to the standard temperature.
Why is API gravity important in the oil industry?
API gravity is one of the most important quality parameters for crude oil pricing and refining. Lighter crudes (higher API) yield more gasoline, diesel, and jet fuel per barrel and require less processing, making them more valuable. Heavier crudes (lower API) need more complex refining and yield lower-value products.