About the Ethanol Blend Fuel Economy
The Ethanol Blend Fuel Economy Calculator shows what an ethanol-blended fuel like E85 or E15 actually costs you per mile, once its lower energy content per gallon is factored in. It's meant for flex-fuel vehicle owners who see a lower price per gallon at the pump for ethanol blends and want to know whether that translates into an actual cost saving once fewer miles per gallon are accounted for.
How It Works
You enter your vehicle's gasoline (E10) MPG, choose whether you're comparing E85 or E15, and provide the price per gallon of both the ethanol blend and regular gasoline. The calculator reduces your gas-car MPG by the blend's energy content relative to gasoline to get an effective MPG on that blend, then divides each fuel's price by its respective MPG to get a cost per mile for both, so you can see which one is actually cheaper to drive.
Examples
E85 at typical station prices
With a 28 mpg gas car, E85's 0.74 energy factor gives an effective 20.7 mpg. At $2.80 a gallon for E85 that works out to about $0.135 per mile, versus $0.125 per mile on gasoline at $3.50 a gallon, meaning the lower price per gallon on E85 doesn't fully offset its lower energy content in this case.
E15 nearly matching gasoline
The same 28 mpg car on E15, with its 0.97 energy factor, gets an effective 27.2 mpg. At $3.30 a gallon for E15 that's about $0.122 per mile, slightly under the $0.125 per mile on $3.50 a gallon gasoline, so E15 comes out marginally cheaper to drive here.
Advantages
- Converts a per-gallon price comparison, which can be misleading, into a per-mile cost comparison, which is what actually determines fuel spending.
- Lets flex-fuel owners quickly check whether a given day's E85 or E15 pricing at the pump is actually worth choosing over gasoline.
- Separates the energy-content effect from the price effect, making clear why a cheaper-looking fuel can still cost more to drive on.
Common Mistakes
- Assuming a lower sticker price per gallon on E85 automatically means cheaper driving, without adjusting for its roughly 26 percent lower energy content.
- Applying blend prices and factors meant for E85 to a vehicle actually running standard E10 gasoline, which isn't the blend this calculator is comparing against.
- Ignoring that MPG on ethanol blends can also vary by engine tuning and driving conditions, not just the fixed energy factor used here.
Edge Cases to Watch For
- The energy factors of 0.74 for E85 and 0.97 for E15 are fixed averages built into the calculator; actual energy content varies somewhat by the specific ethanol percentage and gasoline blend used, so effective MPG for your vehicle may differ slightly.
- If effective MPG works out to zero or less, the calculator sets cost per mile on the blend to zero rather than dividing by an invalid number.
- The note comparing the two fuels flips automatically based on which cost-per-mile figure is lower, so the takeaway message changes with your specific prices, not just the blend type chosen.
Common Use Cases
- Flex-fuel vehicle owners deciding at the pump whether E85 or E15 is worth choosing over gasoline that day.
- Drivers budgeting fuel costs who want to compare blends before a long trip through areas with different fuel pricing.
- Anyone curious why E85's lower per-gallon price doesn't always translate into a lower per-mile cost.