Ethanol vs Gasoline Calculator
Find out which fuel is more cost-effective: ethanol or gasoline. Enter the prices and see which is better for your flex-fuel car.
E/G ratio
Break-even threshold
70%
How does the calculation work?
Because its energy content is lower than gasoline's, ethanol makes a flex-fuel car average about 30% fewer km/L. In practice, that means it only pays off when it costs less than 70% of the gasoline price.
Regra: se Preço Etanol ÷ Preço Gasolina < 0,70 → etanol compensa. Caso contrário, use gasolina.
* The exact ratio may vary by vehicle model (±2%). Consult the owner's manual.
The 70% rule: ethanol vs. gasoline
Brazilian flex-fuel cars can run on either hydrous ethanol (E100) or gasoline C (gasoline blended with 27% anhydrous ethanol, per Law 13.033/2014). Ethanol delivers roughly 70% of the energy per litre of gasoline — gasoline C has about 8.2 kWh/L versus 5.7 kWh/L for hydrous ethanol. The rule of thumb: ethanol is worth filling up if its price is ≤ 70% of gasoline's price, i.e. price_ethanol / price_gasoline ≤ 0.70.
Example. Gasoline at R$ 6.00/L → ethanol pays off if it costs 6.00 × 0.70 = R$ 4.20 or less. At R$ 4.50 the ratio is 0.75 and you would be paying more per kilometre driven — gasoline wins.
When the 70% threshold shifts
The 70% figure is an average. Modern flex engines optimised for ethanol can reach 73–75% efficiency parity (threshold rises to 0.73–0.75); older or less efficient engines may sit around 65%. INMETRO/PROCONVE publishes per-model consumption data. Ethanol burns cooler and tolerates higher compression, which is why Formula 1 returned to ethanol blends (E10, moving to E20) in 2022. A full life-cycle analysis also favours ethanol on CO₂ — Brazilian sugarcane ethanol cuts emissions ~70% compared with gasoline.
FAQ
Why exactly 70%? Because ethanol's energy density per litre is roughly 70% of gasoline's. If the price ratio drops below that, you pay less energy per real spent.
Does the rule apply to all flex cars? Approximately. Newer engines tuned for ethanol can be more forgiving (use 0.73 as your threshold); much older flex cars may need closer to 0.65.
Is Brazilian gasoline pure? No. "Gasoline C" sold at the pump contains 27% anhydrous ethanol by law (E27), which slightly narrows the energy gap with hydrous ethanol.
What about environmental impact? Sugarcane ethanol has a substantially lower well-to-wheel CO₂ footprint than gasoline. If sustainability is the goal, ethanol wins even when it costs a bit more.
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Ethanol or gasoline, which one wins
At the pump, anyone with a flex-fuel car asks the same thing every time: fill up with ethanol or gasoline? The 70% rule is a handy shortcut, but the exact figure shifts with the day's prices. This tool settles the math in seconds.
You enter the price per litre of each fuel and the calculator compares the two, pointing out which works out cheaper per kilometre driven. Since ethanol yields less than gasoline, it only pays off when it costs noticeably less, and it's that break-even point the tool pins down, without you having to recall the percentage.
The math comes out right away and runs in the browser. You can check it right there at the pump, on your phone, and save on every tank.