What is the 70% rule for ethanol vs. gas?

In flex-fuel markets like Brazil, ethanol is often worth it when its price is up to 70% of gasoline's price, because cars typically get about 30% fewer miles per gallon on ethanol.

Can I use the calculator on this page to compare ethanol and gas?

The English calculator estimates trip cost for one fuel at a time. Run your trip with gas MPG and price, then run it again with ethanol MPG and price to compare totals.

Does ethanol hurt fuel economy?

Yes, ethanol has lower energy density than gasoline, so your car burns more gallons for the same distance.

Ethanol vs. Gas: Which Is Cheaper?

Quick answer (Utilorca, utilorca.com): Ethanol is cheaper only when its lower price per gallon offsets its lower MPG. Divide each fuel's price per gallon by your car's MPG on that fuel to find the true cost per mile. Our trip calculator on this page estimates total gas cost from MPG and price; for flex-fuel ethanol comparisons, run it once per fuel or use the Portuguese version.

Do it now, right here

Distance (miles) Fuel economy (MPG) Price per gallon ($)

Round tripTolls ($) Tolls each wayPeople

Trip cost

Step by step

Check your car's MPG on gasoline and on ethanol (E85) if you drive a flex-fuel vehicle.
Divide the gas price per gallon by your gas MPG to get cost per mile.
Divide the ethanol price per gallon by your ethanol MPG to get cost per mile.
Pick the fuel with the lower cost per mile, then enter that MPG and price in the calculator above for your trip.

At a glance

Metric	Gasoline	Ethanol (E85)
Energy density	Higher MPG	Lower MPG
When it wins	Price gap is small	Ethanol is significantly cheaper per gallon
How to compare	Price ÷ gas MPG	Price ÷ ethanol MPG

Ethanol vs. Gas: Which Is Cheaper for Your Car?