E85 Calculator + Online Solver With Free Steps

The E85 Calculator calculates the break-even price per gallon (PPG) for E85 (flex) fuel given the PPG for E10 fuel (gasoline). It helps choose which fuel type to buy as both are commonly available and supported in most automobiles. 

The fuels are differentiated based on ethanol content, with E10 having less than 10% ethanol and E85 between 53 to 85%. They provide the same driving performance, but the E10 offers more miles per gallon (MPG) than the E85. The difference is around 15 to 27% depending on the ethanol content. 

What Is the E85 Calculator?

An E85 Calculator is an online tool that takes the price per gallon (PPG) of E10 fuel (gasoline) and calculates the break-even price per gallon of E85 (flex fuel). 

The calculator interface consists of a single text box labeled E10 (Regular Fuel) Dollar/gallon, into which you enter the price per gallon (in US Dollars) for E10 or gasoline. Once submitted, the calculator shows the results in a new pop-up window with the break-even PPG value for E85 fuel.

How To Use the E85 Calculator?

You can use the E85 Calculator to find the break-even price per gallon of E85 or flex fuel relative to E10 by entering the PPG of E10 fuel. 

For example, suppose the current PPG of E10 is 2.50 USD. Then, you can use the calculator to find the break-even PPG of E85 with the following step-by-step guidelines.

Step 1

Enter the price per gallon (in US Dollars $) of E10 fuel into the text box labeled “E10 (Regular Fuel) $/gallon.” In the example above, this is $2.50 or 2.50 USD. So, you would enter “2.50” here.

Step 2

Press the Submit button to get the results.


The result shows the break-even price per gallon or PPG for E85 fuel. It will always be less than the price entered for the E10 because of the reduced MPG of E85 owing to higher ethanol content. 

For the example, we get the break-even PPG of E85 fuel as 1.8285. You can then compare the actual current PPG of E85 with this value and decide which fuel to use accordingly.

Interpreting the Result

The break-even price per gallon or PPG represents the cost of E85 fuel at which buying it is the same as buying the same amount of E10 in terms of cost per mile.

In other words, it is the price at which a gallon of E85 is economically equivalent to a gallon of E10 – even though the E10 has the better miles per gallon (MPG) rating.

Now, if the actual PPG of E85 fuel is less than the break-even PPG and your vehicle is compatible with it, then you should use E85 instead of E10. You would need to refuel more because of its faster consumption per mile (lower MPG), but it will cost you less in the long run.

On the other hand, if the actual PPG of E85 is greater than the break-even PPG, then you should use E10 instead. You will need to refuel less due to its slower consumption per mile (higher MPG) and save money simultaneously.

How Does the E85 Calculator Work?

The E85 Calculator works by using the formula:

\[ \text{break-even E85 PPG} = 0.7314 \times \text{E10 PPG} \tag*{(1)} \]

The E85 fuel can contain anywhere between 53–85% ethanol, leading to 15–27% reduced MPG relative to E10 fuel. The calculator assumes an 85% ethanol mix in the E85 and a reduced MPG of 26.86%.

Therefore, the E85 PPG should reduce by the same amount relative to the E10 PPG. Thus, the calculator finds the result using the formula:

\begin{align*} \text{break-even E85 PPG} & = (100-26.86) \, \% \times \text{E10 PPG} \\ & = 73.14 \, \% \times \text{E10 PPG} \\ & = 0.7314 \times \text{E10 PPG} \end{align*}

Different E85 Ethanol Concentrations

The calculator will not work if the E85 fuel in your area has a different ethanol concentration like 60 or 70%. However, you can use the result and perform an additional step at your end to get the correct value.

Let c be the ethanol concentration (c = 60 for 60% ethanol), then:

\[ \begin{aligned} \text{break-even E85 PPG} = {} & \text{calculator result} + (0.31735-0.00375 \times c) \\ & \!\! {} \times \text{E10 PPG} \end{aligned} \tag*{(2)} \]

Equation (2) above is derived using linear interpolation and a few mathematical tricks, but it is sure to provide a correct estimate. See how it works in Example 1.

Solved Examples

Example 1

Mr. Smith lives in Texas. He is stuck deciding whether to use E85 or E10 fuel for his car. The current price per gallon of E10 fuel in Texas is 2.65 USD, while that of E85 is 2.10 USD.

Additionally, Mr. Smith plans to move to New Jersey after a year, where both fuels cost the same. However, E85 has a 60% ethanol concentration instead of the 85% in Texas. 

Mr. Smith wants to base his decision entirely on value for money. Help him decide which fuel to use in Texas and which to use in New Jersey.


In Texas

Since the ethanol concentration of E85 fuel is 85% in Texas, we can use equation (1) to get the result directly:

\[ \text{break-even E85 PPG} = 0.7314 \times \text{E10 PPG} = 0.7314 \times 2.65 \text{ USD} \]

\[ \Rightarrow \,  \text{break-even E85 PPG} = \mathbf{1.93821} \textbf{ USD} \]

The calculator also provides this result. Since 2.10 > 1.93821, it is economically more feasible for Mr. Smith to use E10 fuel during his stay in Texas.

In New Jersey

Here, the ethanol concentration is 60%, so let us use equation (2) with c = 60 and our calculator result from the previous scenario:

\[ \text{break-even E85 PPG} = 1.93821 + (0.31735-0.00375 \times 60) \times 2.65 \text{ USD} \]

\[ \text{break-even E85 PPG} = \mathbf{2.18335} \textbf{ USD} \]

Since 2.10 < 2.18335, it is better for Mr. Smith to use E85 fuel during his stay in New Jersey.

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