What is the equation to determine API gravity from specific gravity?

What is the equation to determine API gravity from specific gravity?

• A. API = (131.5 / SG) - 141.5
• B. API = (141.5 / SG) - 131.5
• C. API = SG - 131.5 / 141.5
• D. API = (141.5 * SG) - 131.5

Answer: (B)

API gravity measures how heavy or light a petroleum liquid is compared with water, with higher API meaning lighter oil. Specific gravity is the density of the oil relative to water at 60°F. The standard way to convert SG to API is API = (141.5 / SG) - 131.5. This works because when SG = 1 (density equal to water), API comes out to 10, which matches the convention that water has API close to 10. If the SG is less than 1, API increases, yielding the familiar higher API numbers for lighter crudes (for example, SG ≈ 0.835 gives API ≈ 35). The constants 141.5 and 131.5 are part of the historical relationship that links density to the API scale.

API gravity measures how heavy or light a petroleum liquid is compared with water, with higher API meaning lighter oil. Specific gravity is the density of the oil relative to water at 60°F. The standard way to convert SG to API is API = (141.5 / SG) - 131.5. This works because when SG = 1 (density equal to water), API comes out to 10, which matches the convention that water has API close to 10. If the SG is less than 1, API increases, yielding the familiar higher API numbers for lighter crudes (for example, SG ≈ 0.835 gives API ≈ 35). The constants 141.5 and 131.5 are part of the historical relationship that links density to the API scale.