Advanced Fuel Comparison Form
Formula Used
E85 MPG: Gasoline MPG × (1 − Mileage Loss ÷ 100), or known E85 MPG.
Cost Per Mile: Fuel Price Per Gallon ÷ MPG.
Trip Fuel: Trip Distance ÷ MPG.
Trip Cost: Trip Fuel × Fuel Price Per Gallon.
Break-even E85 Price: Gasoline Cost Per Mile × E85 MPG.
Blend Energy: Ethanol Fraction × Ethanol BTU + Gasoline Fraction × Gasoline BTU.
Range: Tank Size × MPG.
CO2 Estimate: Fuel Used × Blend CO2 Factor.
How to Use This Calculator
Enter the latest gasoline and E85 prices from your local station. Add your gasoline mileage from real driving records. Choose whether to estimate E85 mileage from a loss percentage or use known E85 MPG. Add trip distance, monthly miles, tank size, ethanol content, energy values, and emissions factors. Press the calculate button. Review cost per mile first. Then compare trip cost, yearly savings, range, energy use, and emissions. Use CSV for spreadsheet work. Use PDF for saving or sharing the displayed result.
Example Data Table
| Fuel | Price Per Gallon | MPG | Cost Per Mile | Tank Range |
|---|---|---|---|---|
| Gasoline | $3.60 | 30 | $0.12 | 420 miles |
| E85 | $2.85 | 22.8 | $0.13 | 319.2 miles |
| Break-even E85 | $2.74 | 22.8 | $0.12 | 319.2 miles |
Why Gas and E85 Comparison Matters
Gasoline and E85 behave differently because their chemistry is different. Gasoline carries more energy per gallon. E85 contains a high ethanol share, so it often needs more volume to travel the same distance. A lower pump price can still win, but only when the discount beats the mileage loss. This calculator helps you compare both fuels with the same trip, tank, and driving assumptions.
What the Calculator Reviews
The tool checks price per gallon, expected economy, ethanol content, energy value, range, fuel used, and estimated carbon output. It also estimates the break-even E85 price. That number shows the highest E85 price that matches gasoline cost per mile. You can change ethanol content because real E85 can vary by season and station. You can also enter known E85 mileage when your vehicle already has tested data.
Chemistry Behind the Difference
Ethanol has oxygen inside its molecule. That helps combustion, supports high octane, and can allow aggressive tuning in suitable engines. However, ethanol has lower lower-heating value than gasoline. Less energy per gallon usually means reduced mileage. Flexible fuel vehicles can adjust fuel delivery, but they still need more liquid fuel when ethanol share rises.
How Results Should Be Read
Start with cost per mile. It is the clearest number for daily budgets. Then review trip cost and yearly savings. A negative saving means E85 costs more for your inputs. Range is also important. E85 may require more frequent stops, even when it saves money. Emissions are estimates, not certification values, because refining, farming, transport, and engine tuning can change the true footprint.
Practical Tips
Use recent receipts for accurate prices. Use real mileage from your own driving log when possible. Highway, towing, cold starts, and tire pressure can change both fuels. Compare several E85 discount levels before deciding. A small price change can reverse the best choice. For tuned vehicles, also consider safety, injectors, pump capacity, and manufacturer guidance before using high ethanol blends.
When to Recheck
Run the numbers again when fuel prices move, seasons change, or your route changes. Ethanol blend levels can shift. Your tires, speed, cargo, and weather also affect mileage. Good records make this comparison stronger and clearer over time.
FAQs
1. What does this calculator compare?
It compares gasoline and E85 by price, mileage, trip cost, monthly cost, yearly cost, tank range, blend energy, octane estimate, and estimated carbon output.
2. Why does E85 usually lower mileage?
E85 contains more ethanol. Ethanol has less energy per gallon than gasoline. The engine often burns more fuel volume to produce similar travel distance.
3. When is E85 cheaper than gasoline?
E85 is cheaper when its lower pump price beats the mileage loss. The break-even E85 price shows the highest price that matches gasoline cost per mile.
4. Can I use known E85 mileage?
Yes. Select the known mileage method and enter your tested E85 MPG. This is usually better than using a general mileage loss estimate.
5. What does blend energy mean?
Blend energy estimates the heat value of the fuel mixture. It combines gasoline energy and ethanol energy according to the ethanol percentage entered.
6. Are the CO2 results official?
No. They are estimates based on the factors entered. Real emissions depend on engine design, fuel source, refining, farming, transport, and driving conditions.
7. Why include octane estimates?
Ethanol has high octane. The estimate helps show why E85 can support different tuning strategies in engines designed or modified for it.
8. Should every car use E85?
No. Use E85 only when your vehicle supports it. Check manufacturer guidance before using high ethanol blends in non-flex-fuel vehicles.