Fuel Cost Calculator
A fuel cost calculator estimates how much you will spend on gasoline, ethanol, or diesel for a trip based on three inputs: the distance you will drive, your vehicle's fuel efficiency, and the price per liter or gallon at the pump. Efficiency can be expressed as kilometers per liter (km/L), miles per gallon (MPG), or liters per 100 km, and the calculator converts between them so you can compare vehicles measured in different units.
Fuel is one of the largest variable costs of driving, so estimating it in advance helps you budget road trips, split expenses fairly among passengers, and compare driving against flying or taking a bus. For flex-fuel vehicles common in Brazil, the calculator also answers the classic ethanol-versus-gasoline question: since ethanol contains less energy per liter, it is usually only worth buying when its price is below about 70% of the gasoline price.
How it works
Fuel cost = (distance ÷ fuel efficiency) × price per unit of fuel. For example, a 450 km trip in a car that does 12 km/L with fuel at $1.20 per liter needs 450 ÷ 12 = 37.5 liters, costing 37.5 × 1.20 = $45.00. With MPG, divide miles by MPG to get gallons, then multiply by the price per gallon. For ethanol comparison, the tool checks whether ethanol price ÷ gasoline price is below 0.70 — the approximate energy-equivalence break-even for flex-fuel engines.
Use cases
- Budgeting the fuel cost of a road trip before you leave and splitting it among passengers
- Comparing whether ethanol or gasoline is cheaper per kilometer in a flex-fuel car
- Estimating monthly commuting costs from your daily round-trip distance
- Comparing the running cost of two vehicles with different fuel efficiency before buying
Frequently asked questions
How do I calculate fuel cost for a trip?
Divide the trip distance by your car's fuel efficiency to get the fuel volume, then multiply by the price per liter or gallon. For example, 300 miles at 30 MPG uses 10 gallons; at $3.50 per gallon the trip costs $35. Remember to double the distance for a round trip.
When is ethanol worth it instead of gasoline?
Ethanol delivers roughly 70% of the energy of gasoline per liter, so a flex-fuel car travels fewer kilometers on each liter of ethanol. As a rule of thumb, ethanol is only economical when its pump price is below about 70% of the gasoline price. Divide the ethanol price by the gasoline price: below 0.70, fill up with ethanol.
How do I convert MPG to km/L?
Multiply MPG by 0.4251 to get km/L (1 mile = 1.609 km and 1 US gallon = 3.785 L). So 30 MPG equals about 12.75 km/L. To convert to the European measure of L/100 km, divide 235.21 by the MPG value: 30 MPG ≈ 7.84 L/100 km.
What affects my car's real-world fuel consumption?
Speed, driving style, and load matter most: aggressive acceleration, speeds above about 100 km/h (62 mph), underinflated tires, roof racks, and air conditioning can each raise consumption noticeably. City stop-and-go traffic typically consumes 20-40% more fuel per kilometer than steady highway driving.
Should I use city or highway fuel efficiency in the calculation?
Use the figure that matches your route: highway efficiency for long trips on open roads, city efficiency for urban commutes, or a weighted mix for combined routes. Real-world numbers are usually 10-20% worse than official laboratory ratings, so measuring your own average over a few tank fills gives the most accurate estimate.