Enter both pump prices and see which one costs less per mile. E85 is cheaper per gallon and goes fewer miles on it — the answer depends on how much cheaper.
E85 is sold at roughly 2% of US stations, most of them in the Midwest. Many flex-fuel owners do not know they have one — check for a yellow fuel cap or the badge on the tailgate.
70% is the classic figure. Newer flex-fuel engines often reach 73–75% — if you know your own mileage, the answer becomes exact.
Cheaper to fill up with
With both figures the efficiency above comes from your car instead of a table. It is the precise way to answer the question.
A gallon of ethanol carries about a third less energy than a gallon of gasoline, so a flex-fuel vehicle running E85 covers fewer miles on the same gallon — typically 70% to 75% of what it would do on regular. E85 is also priced lower at the pump, and the whole question is whether the discount covers the shortfall. Divide the E85 price by the gasoline price: if the result is below your vehicle’s efficiency figure, E85 wins the mile.
The calculation itself has no units in it. It compares one ratio against another — price against efficiency — so gallons, litres, dollars and euros all cancel out. The only thing that matters is that both prices are quoted the same way. Two prices per gallon work; a price per gallon against a price per litre gives a number that means nothing.
Availability is the real constraint in the United States, not the arithmetic. Roughly 2% of stations sell E85, and they cluster heavily in the Midwest — Minnesota, Iowa and Nebraska have hundreds each, while several states have a handful. If you have the choice at all, you probably already know where the pump is.
A surprising number of drivers own a flex-fuel vehicle without knowing it. Around twenty million are on the road, and the badge is easy to miss. Check for a yellow fuel cap or a yellow ring inside the filler door, look for an E85 or FlexFuel badge on the tailgate, or check the owner’s manual. Putting E85 in a car that is not flex-fuel is a different matter entirely, and not something to try.
Divide the E85 price by the gasoline price. If E85 is $2.59 and regular is $3.29, that is 0.79 — above a typical 0.73 efficiency, so gasoline costs less per mile despite the cheaper pump. Below your vehicle’s figure, E85 wins. The calculator above does this with the numbers you enter.
Most flex-fuel vehicles return 70% to 75% of their gasoline MPG on E85, because ethanol holds less energy per gallon. Some engines tuned for high octane do better than that. The only figure that describes your car is the one you measure.
Fill up on gasoline only, reset the trip meter, and note the miles per gallon on the next fill. Repeat on E85. Divide the E85 MPG by the gasoline MPG — 24 MPG on gas and 17.5 on E85 gives 0.729. Enter both figures above and the calculator does the division.
No. Only a flex-fuel vehicle is built for it, with fuel-system components and engine mapping that tolerate high ethanol. Look for a yellow fuel cap, a FlexFuel or E85 badge, or check the owner’s manual. If the car is not flex-fuel, E85 does not belong in the tank.
About 2% of US stations sell it, concentrated in the corn-producing Midwest — Minnesota, Iowa, Nebraska, Illinois and Indiana hold most of them. Coverage in the Northeast and the Mountain West is thin. The US Department of Energy maintains a public station locator.
No. The calculation runs in your browser and there is no server for anything to be sent to.
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