E85 Calculator - Ethanol Mix

How to use this Calculator

Use this calculator for these situations:

  • You have a completely empty fuel tank, and plan on filling up with a specific ethanol/gas mixture
  • You already have an ethanol mixture in the tank, and want to fill up while keeping the same mixture (i.e. you have E30 in the tank and want to add ten more gallons of E30)
  • You aren't as concerned with precise mixtures, octane ratings, or need to make any manual adjustments to the fuel specifics
Enter the number of total amount of fuel you need to fill up with in the "Gallons to Fill" box. Then, select your desired mixture in the dropdown - if you have a custom tune from us, we most likely specified something like "E30" or "E50" to use. Now press the "Calculate Mix" button, and the results are displayed to the right. Simply add the amount specified by each fuel type to achieve that mixture.
This calculator also makes the following assumptions:
  • Your E85 fuel has an ethanol content of 85%
  • Your Gasoline has an ethanol content of 10%

 

Gallons To Fill: Desired Ethanol Mix:

E85 Gallons: ?
Gas Gallons: ?
For every 1 Gallon of Ethanol, add ? Gallons of Gasoline.

Advanced Calculator

Use this calculator for these situations:

  • You already have some gasoline in your tank, and want to add some ethanol to achieve a desired mixture
  • You are interested in calculating the estimate octane in different mixture amounts
  • Fuel in your area has different ethanol contents - for example, "E85" with 70% ethanol, or pure gasoline with 0% ethanol, etc
For the first (and likely most common) scenario, simply enter the number of gallons of gasoline you think you have in your fuel tank, to your best approximation. Then, add in a number for gallons of ethanol and click the "calculate fuel" button. This will display your specific ethanol mixture - E30, E35, E36, etc. If your desired ethanol mix is lower, decrease the gallons you entered for "E85 Gallons" and click the "calculate fuel" button again. Use this to estimate how much E85 you will need to put in to get the desired mixture.

 

Starting from the left column:
  • E85 Gallons - the amount of E85 fuel to be used
  • Gas Gallons - the amount of gasoline to be used
For the center column:
  • E85 Octane - This can fluctuate based on the fuel station. In the US, it is usually rated anywhere from 100 to 105 octane, but it should display the exact number on the pump.
  • Gas Octane - Enter your gasoline's octane here. The mixture still benefits from using higher octane gas, since the limiting factor is the ethanol content of the fuel, not the octane. Adding ethanol is not a substitute for higher octane gasoline, it should be added to increase the octane of an already premium fuel (preferably 93US / 98RON, but 91US / 95RON will do). For example, using 87 octane gas to make an E30 mixture results in an octane rating similar to plain premium gas, but with a higher price, hassle of mixing, and lower fuel economy.
For the right column:
  • E85 Ethanol % - This is the exact ethanol content of the fuel you are using. In the US, "E85 fuel" isn't always 85% ethanol, it can be anywhere from 51%-85%. The fuel provider should show the ethanol content of each fuel at the pump.
  • Gas Ethanol % - Most gasoline in the US has around 10% ethanol content. If you have access to ethanol-free gas, change this number to 0, or adjust as necessary.
After filling out each box (default values already placed for you), click the "Calculate Fuel" button. This will fill out the bottom row with the calculated results, showing the total number of gallons specified, the estimated octane rating of the fuel mixture, and the ethanol content amount.

 

Special note for non-US customers: fuel in the US is measured with the formula (RON+MON)/2. Most fuels elsewhere are measured only in RON (98 RON, 95RON, etc). This does not affect the calculations - simply enter in the octane of your local petrol and ethanol fuels and it will return the correct result (in RON).

E85 Gallons: E85 Octane: E85 Ethanol %:
Gas Gallons: Gas Octane: Gas Ethanol %:
Total Gallons: ? Octane Rating: ? Ethanol Mixture:?

Note: All data extrapolated from these calculators are purely estimates. While we strive to provide accurate data, we are not liable for any damages, issues, or incidents caused by the use of the tools provided on our website.