Fuel & Trip Cost Calculator

From vehicle consumption to a final cost

A trip's cost depends on three numbers: distance, vehicle consumption (km/l or mpg), and fuel price. The tool divides distance by consumption to find how many liters (or gallons, in miles mode) are needed, then multiplies that by the price you entered to reach the total cost. Checking round trip simply doubles the distance before that calculation, and entering more than one passenger splits the total cost across that number of people.

There is no currency conversion involved: the fuel price is just a number you type in your own currency, so the result comes out in the same monetary unit you used for the price.

• Fuel needed = distance ÷ consumption.
• Total cost = fuel needed × fuel price.
• Round trip = distance × 2, before computing fuel.
• Cost per person = total cost ÷ number of passengers.

The 70% rule, and the energy math behind it

Hydrous ethanol, the fuel Brazilian flex-fuel cars run on, holds roughly 30% less energy per liter than gasoline, so a flex engine has to burn more ethanol than gasoline to cover the same distance. That energy gap is the practical reason behind Brazil's well-known 70% rule, widely cited by fuel-industry federations and used as a household rule of thumb: ethanol only pays off when its price sits below roughly 70% of the gasoline price. If the ethanol-to-gasoline price ratio is under 0.70, ethanol tends to be cheaper per kilometer; at or above that, gasoline tends to win.

The 70% rule is only a national average, though. Different flex engines have different real-world efficiency on each fuel, newer engines with optimized injectors, older engines, and turbo flex engines don't all behave the same way. That's why, whenever you know your own car's real consumption on gasoline and on ethanol, the tool automatically switches to the precise calculation: cost per km for each fuel, computed straight from your car's mileage, with no dependence on any rule of thumb. The same underlying idea applies outside Brazil too: any lower-energy-density fuel needs to be cheap enough, relative to its energy content, to beat a higher-energy-density one.

• Ratio = ethanol price ÷ gasoline price.
• Ratio below 70%: ethanol tends to pay off.
• Ratio at or above 70%: gasoline tends to pay off.
• With real mileage entered, cost per km decides, not the price ratio.

Limits of the comparison

Neither the 70% rule nor the real-mileage calculation accounts for engine wear, oil costs, tolls, travel time, or emissions, the focus is fuel cost alone. Manufacturer-listed consumption figures are usually measured under controlled conditions and tend to be more optimistic than real-world daily driving, so where possible, use the mileage you measured yourself on your own car (distance driven divided by liters filled) instead of the factory figure.

Fuel prices vary by station, brand, region and over time, so it's worth double-checking current prices before deciding. Nothing you type into this tool is sent to any server, every calculation runs in your browser.