In the United States the "octane" rating of a gasoline is based on the anti-knock index (AKI). This reflects the tendency of the fuel to burn in a controlled manner. The greater the tendency to burn in a controlled manner, the less the amount of engine knocking and the greater the engine's efficiency.



(1) Research Octane Number (RON)

(2) Motor Octane Number (MON)


The RON and MON compare a fuel to a mixture of iso-octane and heptane under different conditions (RON performed at 600 rpm and MON at 900 rpm, plus other differences).


In both scales a 0 is equivalent to 100% heptane and 100 is equivalent to 100% iso-octane.


Usually the RON is 8-10 points higher than the MON.


anti-knock index =

= ((RON) + (MON)) / 2


To read more or access our algorithms and calculators, please log in or register.