What Is an Octane Mixing Calculator?
An Octane Mixing Calculator estimates the octane rating of a blend made from two fuels with different octane ratings. It uses each fuel's quantity to calculate a volume-weighted average.
For example, mixing equal quantities of fuel rated at 87 and 93 gives a simple mathematical estimate of 90 octane.
Octane Mixing Formula
When using a simple linear mixing estimate, multiply each fuel's octane rating by its quantity, add the two results and divide by the combined fuel quantity.
Blended Octane = [(Octane 1 × Quantity 1) + (Octane 2 × Quantity 2)] ÷ (Quantity 1 + Quantity 2)
How Does the Octane Mixing Calculator Work?
Enter the octane rating and quantity of each fuel. The calculator determines the total quantity, percentage contributed by each fuel and estimated blended octane rating.
Enter First Fuel
Add the octane rating and quantity of the first fuel.
Enter Second Fuel
Enter the octane rating and quantity for the second fuel using the same volume unit.
View the Estimate
Review blended octane, total volume and the percentage contribution of each fuel.
Octane Mixing Example
Suppose you combine 5 gallons of 87-octane fuel with 5 gallons of 93-octane fuel.
Example Calculation
Under the simple weighted-average assumption, the resulting blend is estimated at 90 octane.
Can You Mix Different Octane Fuels?
The calculator can mathematically compare blends of two different octane ratings. However, the suitability of a particular fuel for a vehicle depends on the fuel specification required by the manufacturer.
Octane rating describes a gasoline fuel's resistance to auto-ignition or knock under standardized testing. A higher octane number does not simply mean that a fuel contains more energy.
Octane Rating
The octane number indicates resistance to engine knock under the applicable rating system.
Blend Percentage
The calculator shows what percentage of the final volume comes from each of the two entered fuels.
Why the Quantity of Each Fuel Matters
The final estimate depends on both octane ratings and the amount of each fuel. If one fuel represents a larger percentage of the total volume, its octane rating has a larger influence on the weighted-average result.
For example, a mixture containing mostly 93-octane fuel and only a small quantity of 87-octane fuel will have an estimated rating closer to 93 than 87.
RON, MON and AKI Should Not Be Mixed as Equivalent Numbers
Octane values can be reported using different rating systems. Research Octane Number (RON), Motor Octane Number (MON), and Anti-Knock Index (AKI) are not interchangeable numerical scales.
For a meaningful weighted-average calculation, both octane values should be expressed using the same rating system. For example, compare RON with RON or AKI with AKI rather than treating different rating systems as identical.
This calculator uses a linear volume-weighted average. Real gasoline blending behavior can be non-linear because actual octane response depends on fuel composition and blend properties. Use published fuel specifications or qualified technical guidance when an exact fuel rating is required.
Gallons vs Litres in Octane Mixing
You can use gallons, litres, quarts or millilitres with this calculator. The important requirement is that both fuel quantities use the same unit.
Because the formula works from the relative quantities, the estimated octane result is unchanged when both quantities are consistently converted to another volume unit.
Common Octane Mixing Calculation Mistakes
- Using different volume units for the two fuel quantities.
- Averaging the octane numbers without considering unequal quantities.
- Treating RON and AKI values as directly equivalent.
- Assuming the mathematical estimate guarantees actual blend performance.
- Ignoring the vehicle manufacturer's required fuel specification.
Octane Mixing Calculator FAQs
For a simple weighted estimate, multiply each octane rating by its fuel quantity, add the results and divide by the total fuel quantity.
A simple linear weighted-average calculation gives an estimated octane rating of 90 when equal quantities of 87 and 93 are used.
Yes. You can use litres, gallons, quarts or millilitres as long as both fuel quantities use the same unit.
No. This calculator provides a volume-weighted mathematical estimate. Actual gasoline blending can show non-linear behavior depending on fuel composition.
The two octane inputs should use the same rating system. RON and AKI are different rating systems and should not be treated as numerically equivalent.
Octane rating primarily describes resistance to knock under standardized testing. It is not simply a measurement of the fuel's energy content.