Calculate Ethanol % of Mixture

This calculator will calculate the octane and percent of ethanol from a mixture of E85/Ethanol and gasoline.
(one could use straight ethanol or even methanol, use appropriate octane rating)

Got an email asking how to figure out the amount of 100% Ethanol to add to a mixture that is below E85 rating.
It may take some trial fitting to see what the amount is.
Try putting 100 (for percent) in the left side percentage input.
And try .25 for the 'gallon' amount in the left side inputs.
In the right side, input 1 for gallons and use your percentage of ethanol in your fuel.
Click the Calculate button.

This should give the amount of Ethanol percentage of the new mixture.
If the answer is not 85 (for E85) try changing the gallon amount of the left side. (.25 posted above)
Make it larger if the percent is lower than 85.

When it says E85, the amount inputted in the gallon on left side
is amount to add to 1 gallon of your original percentage.

The Octane Rating in the calculator is using (R+M)/2 values.
You can use your octane value (like RON), the answer will be in your octane value.

Calculate Ethanol % of Mixture
Fuel Mix
(Ethanol) Octane:
% Ethanol:
Fuel Mix
Gas Octane:
% Ethanol:
Input All Data, Please

The equivalent octane of E85 can be from 105 to 109 or so.
The equivalent octane of 100% ethanol is around 113-115.
(there is no 'octane' additive like in gasoline, in ethanol or methanol)