E85 Flex-Fuel Calculator
Gas vs E85 prices to per-mile winner.
What it does
E85 stickers run cheaper per gallon while delivering fewer miles per gallon, so pump price lies. Energy near 73 % of gasoline means cost per mile decides every fill. Two divisions settle it.
The tool above prices gas and E85 per mile from pump prices and gas economy, then names the winner. A $2.20 E85 against $3.50 gas at 25 mpg wins by almost two cents a mile.
Energy department flex-fuel resources with fuel-economy guides publish the same energy share and comparison method. Winter blends lean out for cold starts, narrowing the gap seasonally.
Check flex-fuel badges before chasing discounts: conventional fuel systems corrode on high ethanol. Then compare per mile, map E85 stations ahead, and recheck as spreads swing.
How to use
- Enter regular gas price.
- Enter E85 price.
- Enter gas mpg for the car.
- Read cost per mile each.
- Read the winner verdict.
- Confirm flex-fuel capability first.
Formula
- gas
- Regular gasoline price per gallon.
- E85
- E85 price per gallon.
- mpg
- Car economy on gasoline.
Energy share 73 % is the standard planning assumption; winter blends run higher ethanol-lean. Per-mile costs divide each fuel price by its economy. Driving style moves both equally.
Worked example
Example: $3.50 vs $2.20
$3.50 gas vs $2.20 E85 at 25 mpg gas economy.
- Gas is $3.50, E85 is $2.20, car makes 25 mpg on gas.
- Gas cost: 3.50 / 25 = 0.140 $/mi.
- E85 economy: 25 x 0.73 = 18.25 mpg.
- E85 cost: 2.20 / 18.25 = 0.121 $/mi.
- E85 wins this fill by almost two cents a mile.
Reference table
| Gas price | E85 must beat | Discount |
|---|---|---|
| $3.00 | $2.19 | 27 % |
| $3.50 | $2.56 | 27 % |
| $4.00 | $2.92 | 27 % |
| $4.50 | $3.29 | 27 % |
Limits
- 73 % planning factor; winter blends differ.
- Same driving assumed both fuels.
- Station availability limits reality.
- Flex-fuel vehicles only.
Common mistakes
- Comparing gallon prices directly.
- Running E85 in conventional cars.
- Forgetting winter blend shifts.
- Ignoring station detours.
- Assuming the spread holds.
Try it yourself
Quick checks. Answers sit tucked under each question.
$4.00 gas vs $3.20 E85 at 30 mpg?
Gas is 4.00 / 30 = 0.133 $/mi. E85 runs 21.9 mpg: 3.20 / 21.9 = 0.146 $/mi. Gasoline wins.
$3.00 gas vs $2.00 E85 at 20 mpg?
Gas is 3.00 / 20 = 0.15 $/mi. E85 runs 14.6 mpg: 2.00 / 14.6 = 0.137 $/mi. E85 wins.
Questions
Why does E85 need a discount?
About 73 % of gasoline energy, so miles per gallon drop roughly a quarter on E85. Cost per mile decides, not price per gallon.
How do I compare fairly?
Divide each price by its miles per gallon: gas price over gas mpg versus E85 over 73 % of it. Lower cents per mile wins regardless of sticker.
What discount makes E85 win?
Roughly 27 % cheaper than gas to break even at equal driving. Smaller gaps favor gasoline; bigger gaps favor E85.
Can any car use E85?
Flex-fuel vehicles with yellow caps and E85 badges; check the manual and fuel door. Conventional cars must never run it.
Does the blend change by season?
Yes: winter blends drop toward E51 for cold starts, cutting the energy gap and the needed discount. Summer E83 demands the full spread.
Where do I find E85?
Available at select stations, clustered in corn states. Range apps map pumps; never assume the next exit carries it.