A fuel comparison calculator tells you whether gasoline or ethanol is the better deal at today's prices - applying the 70% rule that accounts for the lower energy density of ethanol.
The Gasoline vs Ethanol Decision
Ethanol and gasoline are priced differently at the pump, but ethanol produces less energy per liter (or gallon) than gasoline. A car running on ethanol travels fewer kilometers per liter than the same car on gasoline.
This means a lower price per liter does not automatically make ethanol the better deal. You need to compare on a fuel efficiency-adjusted basis.
The 70% Rule
The standard rule used in Brazil (where flex-fuel vehicles are common) and useful for any ethanol comparison is:
Ethanol is worth it if its price is 70% or less of the gasoline price.
If ethanol costs more than 70% of gasoline's price per liter, gasoline is more economical.
Formula: Ethanol/Gasoline ratio = Ethanol price / Gasoline price
- If ratio < 0.70 → choose ethanol
- If ratio > 0.70 → choose gasoline
- If ratio = 0.70 → break even
How to Use the Fuel Comparison Calculator
- Open the Fuel Comparison Calculator on UtilWave.
- Enter the current gasoline price per liter (or gallon).
- Enter the current ethanol price per liter (or gallon).
- The calculator instantly tells you which fuel is more economical and the ratio.
Example Calculation
If gasoline costs $5.00/gallon and ethanol costs $3.20/gallon:
- Ratio = 3.20 / 5.00 = 0.64 (64%)
- Since 0.64 < 0.70, ethanol is the better choice
If gasoline costs $5.00/gallon and ethanol costs $3.80/gallon:
- Ratio = 3.80 / 5.00 = 0.76 (76%)
- Since 0.76 > 0.70, gasoline is the better choice
Why 70%?
Ethanol has about 70% of the energy content of gasoline by volume. A flex-fuel vehicle running on pure ethanol (E100) gets roughly 30% fewer kilometers per liter compared to gasoline. So you need ethanol to cost at least 30% less per liter to break even.
The 70% threshold is a well-established approximation. Some engines are slightly more or less efficient on ethanol - the actual break-even point varies between 68% and 72% depending on the specific vehicle.
Environmental Considerations
Ethanol has a lower carbon footprint than gasoline over its full lifecycle when produced from sugarcane (as in Brazil). From corn (US ethanol), the environmental benefit is smaller. Price efficiency and environmental impact are separate considerations.
FAQ
Does this apply to E10 or E15 blends? The 70% rule applies to pure ethanol (E100) vs pure gasoline. For lower blends like E10 or E15, the energy difference is smaller, so the break-even ratio is higher (closer to 90%+ for E10).
My car does not have a flex-fuel engine - does this matter? If your car runs only on gasoline, this calculator does not apply. Flex-fuel vehicles are required to benefit from the ethanol option.
Is there a different rule for E85? E85 (85% ethanol, 15% gasoline) has about 73–83% of gasoline's energy content depending on the exact blend. A general rule for E85 is that it should cost 72–80% of gasoline to break even.
What if prices change daily? Check prices before each fill-up. The calculation is quick and takes seconds with this tool.
Compare fuel prices instantly with the free Fuel Comparison Calculator.