Enter the specific gravity at 60°F and the aniline point in °F into the calculator to determine the Cetane Index. This calculator can also evaluate any of the variables given the others are known.

Cetane Index Formula

The following formula is used to calculate the Cetane Index.

CI = (454.54 - 1640.6 * SG) + (774.74 * A) - (0.554)


  • CI is the Cetane Index
  • SG is the specific gravity at 60°F
  • A is the aniline point in °F

To calculate the Cetane Index, subtract 1640.6 times the specific gravity at 60°F from 454.54. Then, add 774.74 times the aniline point in °F. Finally, subtract 0.554 from the result.

What is a Cetane Index?

The Cetane Index is a measure of the combustion speed of diesel fuel and compression needed for ignition. It indicates the quality of diesel fuel, with a higher index indicating better quality. The index is important for reducing knocking noise in the engine, improving fuel efficiency, and reducing harmful emissions. Diesel fuels with a higher cetane index are more desirable as they cause the fuel to ignite more quickly when injected into the combustion chamber.

How to Calculate Cetane Index?

The following steps outline how to calculate the Cetane Index:

  1. First, determine the specific gravity at 60°F (SG).
  2. Next, determine the aniline point in °F (A).
  3. Next, gather the formula from above = CI = (454.54 – 1640.6 * SG) + (774.74 * A) – (0.554).
  4. Finally, calculate the Cetane Index.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

specific gravity at 60°F (SG) = 0.85

aniline point in °F (A) = 120