Ethanol vs Gasoline Calculator (Brazil’s 70% Rule)
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Almost every car sold in Brazil is flex-fuel, so drivers face a decision at every fill-up: ethanol or gasoline? Enter both pump prices and this calculator applies the classic 70% rule, showing the break-even ethanol price and how much you save per equivalent liter. Defaults are the ANP national averages for the week of August 2–8, 2026.
Why 70% is the magic number
Hydrous ethanol carries less energy per liter than the gasoline sold in Brazil, so a flex-fuel car typically travels about 70% as far on a liter of ethanol as it does on a liter of gasoline. If ethanol delivers 70% of the range, it only makes financial sense when it costs at most 70% of the gasoline price.
The rule is elegant because it needs no information about your car’s fuel economy. Divide the ethanol price by the gasoline price: below 0.70, fill up with ethanol; above 0.70, fill up with gasoline. That ratio is the first line of the result panel.
Modern flex engines with direct injection and high compression ratios extract more from ethanol’s higher octane and reach 72%–75% relative efficiency, which pushes the threshold closer to 75%. That is why the calculator lets you switch between the two assumptions.
September 2026 reference prices
Brazil’s petroleum regulator, ANP, surveys pump prices in more than 2,700 municipalities every week. In the week of August 30 – September 5, 2026, hydrous ethanol averaged R$3.95 per liter nationally — cheaper in 13 states, dearer in 12 and flat in Piauí and the Federal District — while regular gasoline averaged R$6.51 per liter. That puts the national ethanol-to-gasoline parity at 60.68%, comfortably inside the 70% threshold.
National averages hide enormous regional spread. The cheapest ethanol recorded that week was R$2.89 per liter at a station in São Paulo; the most expensive was R$6.59 in Pernambuco. By state average, São Paulo was cheapest at R$3.70 and Amapá dearest at R$5.81. The best state-level parities were Mato Grosso at 56.91% and São Paulo at 58.00% — both major ethanol-producing states, where short freight distances keep the biofuel cheap.
| Gasoline price | Ethanol worth it up to (70%) | Ethanol worth it up to (75%) |
|---|---|---|
| R$5.50 | R$3.85 | R$4.13 |
| R$6.00 | R$4.20 | R$4.50 |
| R$6.50 | R$4.55 | R$4.88 |
| R$7.00 | R$4.90 | R$5.25 |
| R$7.50 | R$5.25 | R$5.63 |
| R$8.00 | R$5.60 | R$6.00 |
Where ethanol wins in Brazil
Ethanol economics in Brazil follow the crop. In the Center-South producing states — São Paulo, Mato Grosso, Mato Grosso do Sul, Goiás, Minas Gerais and Paraná — supply is abundant and freight is short, so parity stays below 70% for most of the year. In the North and Northeast, fuel travels thousands of kilometers and logistics costs usually push parity above the threshold.
There is also a seasonal pattern. From April to November the sugarcane harvest floods the market and ethanol gets more competitive; between December and March, during the off-season, parity climbs again. The practical takeaway is to re-run the calculation at each fill-up rather than deciding once and forgetting about it.
What the rule leaves out
The 70% rule answers only the immediate cost question. Ethanol delivers slightly more power and torque thanks to its higher octane, and its life-cycle carbon footprint is far lower because sugarcane absorbs CO₂ while growing. On the other hand, older flex cars rely on a small auxiliary gasoline reservoir for cold starts, and ethanol is more corrosive in vehicles that sit unused for long periods.
Switching between the two fuels tank by tank is completely safe — flex engines detect the blend and adjust injection automatically.
Frequently asked questions
Does the 70% rule still hold in 2026?
Yes, as a quick and conservative benchmark for most of Brazil’s fleet. The caveat is that recent flex engines with direct injection and high compression reach 72%–75% relative efficiency, so their true break-even sits closer to 75%. The calculator lets you pick the assumption that fits your car.
Can I mix ethanol and gasoline in the same tank?
Mechanically, yes — flex engines read the blend and adapt on their own. Financially there is no advantage: your cost per kilometer simply lands between the two. If one fuel clearly wins under the 70% rule, fill up entirely with that one.
Can a gasoline-only car run on hydrous ethanol?
No. Non-flex engines lack the sensor and injection mapping for ethanol and can suffer serious fuel-system damage. Only vehicles badged as flex (widely sold in Brazil since 2003) can use hydrous ethanol.
How much money does choosing correctly actually save?
At early-September 2026 national averages and 70% relative efficiency, ethanol costs about R$0.87 less per gasoline-equivalent liter — roughly 13% of the fuel bill. A driver covering 1,500 km per month in a car doing 10 km/l on gasoline would save around R$130 monthly.
Sources
Default prices come from ANP’s weekly fuel price survey for the week of August 30 – September 5, 2026 (regular gasoline R$6.51/L and hydrous ethanol R$3.95/L, national resale averages). Prices vary widely by state, city and station — always re-run the numbers with the prices on the pump. Real relative efficiency depends on the engine, its condition and your driving pattern.
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Also available in Portuguese: Álcool ou Gasolina: qual compensa abastecer?