Octane Mixing Calculator

About this calculator

Mixing two fuels of different octane ratings produces a blend whose octane is approximately the volume-weighted average of the two: blend octane = (volume₁ × octane₁ + volume₂ × octane₂) ÷ (volume₁ + volume₂). This linear "splash blending" approximation is what most pump-fuel mixing calculations use, though real octane blending can show small non-linear synergy or antagonism effects between certain fuel components that the simple average does not capture.

Drivers who mix premium and regular fuel to hit a specific octane target — common when a car's manual specifies a minimum octane that falls between two pump grades, or when track-day drivers blend in racing fuel — use this calculation to know roughly what octane rating they end up with, since guessing wrong can mean running an engine on fuel below its knock-resistance requirement.

This calculator takes the volumes and octane ratings of your two fuels and returns the resulting blend's octane rating, so you can mix confidently to hit a target number.