Fuel Cost Calculator
Calculate how much fuel a trip will cost from the distance, your vehicle's efficiency, and the price at the pump.
How to use this calculator
- 1Choose your unit system.
- 2Enter the trip distance, your vehicle's efficiency, and the current fuel price.
- 3Turn on round trip if you need the cost for the return leg too.
How the calculation works
US: Fuel = Distance ÷ MPG. Metric: Fuel = (Distance ÷ 100) × L/100km. Cost = Fuel × Price- MPG
- Miles per gallon — higher means more efficient
- L/100km
- Litres per 100 km — lower means more efficient (the opposite direction from MPG)
MPG and L/100km measure efficiency in opposite directions — one is distance per unit of fuel, the other is fuel per unit of distance — which is why they use different formulas here rather than a simple unit conversion.
Worked example
500-mile trip at 30 MPG, $3.50/gallon
- 1.Fuel needed: 500 ÷ 30 = 16.67 gallons.
- 2.Cost: 16.67 × $3.50 = $58.33.
Result: $58.33
What MPG and L/100km actually measure
The two common efficiency ratings measure the same underlying thing — how much fuel it takes to move a vehicle a given distance — but express it in opposite directions. MPG (used in the US and UK) is distance per unit of fuel, so a bigger number means better efficiency. L/100km (used across most of the rest of the world) is fuel per fixed distance, so a smaller number means better efficiency. Neither is more "correct"; they answer the same question from opposite ends.
That inversion has a real consequence: equal-sized MPG improvements are not equally valuable. Going from 10 MPG to 20 MPG on a given trip cuts fuel used in half, but going from 30 MPG to 40 MPG only cuts it by a quarter, even though both are "10 MPG better." Because MPG is the reciprocal of actual fuel consumption, the gains bunch up at the low end of the scale — which is exactly why L/100km, a straight linear measure of fuel burned, is often the more intuitive number for comparing two efficient vehicles.
What actually changes fuel consumption on a real trip
A vehicle's rated efficiency is a lab figure under controlled conditions. Real trips diverge from it for reasons that are mostly under a driver's control.
- Speed — aerodynamic drag rises with the square of speed, and the power needed to overcome it rises even faster — which is why fuel economy typically peaks somewhere in the 45–65 mph range and falls off noticeably above it, well before any legal limit.
- Load and cargo — extra weight in the cabin or trunk takes more energy to accelerate, and anything mounted on a roof rack adds drag on top of that — a loaded roof box can measurably hurt highway economy on its own.
- Tire pressure — underinflated tires increase rolling resistance, making the engine work harder for the same distance. It is one of the few efficiency factors that costs nothing to fix.
- Terrain and elevation change — climbing costs more fuel than descending recovers, so a hilly round trip nearly always costs more than the same flat distance, even though the net elevation change is zero.
- Stop-and-go traffic and idling — repeated acceleration from a stop uses far more fuel than maintaining a steady speed, and idling burns fuel while covering no distance at all — city driving is reliably less efficient than highway cruising for this reason.
- Climate control and cold starts — air conditioning draws noticeable engine power, and a cold engine runs less efficiently for the first several minutes after starting — short trips in extreme temperatures see the biggest gap between rated and real-world efficiency.
Practical ways to lower the cost of a trip
None of these change the price at the pump, but each one changes how much fuel a given trip actually consumes.
- Combine errands — a single trip covering several stops avoids repeated cold starts, which are one of the least efficient parts of any drive.
- Drive smoothly — gentle acceleration and anticipating stops (rather than braking hard and re-accelerating) reduces the energy wasted to heat in the brakes.
- Keep the vehicle maintained — correct tire pressure, a clean air filter and up-to-date service all keep the engine and drivetrain working as efficiently as it was rated.
- Shed unnecessary weight and drag — remove cargo and roof racks that are not actually needed for the trip.
- Time and route the trip — avoiding peak congestion keeps a drive closer to steady-speed cruising instead of stop-and-go traffic.
Comparing fuel types
Gasoline, diesel and electricity are priced and measured differently, which makes a direct cost comparison less obvious than it first appears. Diesel engines typically achieve higher fuel economy than an equivalent gasoline engine because diesel fuel carries more usable energy per gallon and diesel engines run at a higher compression ratio, though diesel itself is often priced differently than gasoline depending on the market and season. Electric vehicles sidestep the comparison entirely, since their running cost is usually expressed in energy price per mile or per kilowatt-hour rather than a fuel-volume figure like MPG or L/100km — a genuinely different unit that this calculator does not attempt to convert between.
What this assumes, and where it stops
Assumptions
- Fuel efficiency stays constant across the whole trip — real efficiency varies with speed, terrain, load and traffic.
Limitations
- Does not account for tolls, parking or other trip costs — fuel only.
Common questions
Why is my actual fuel cost different from the estimate?
Real-world MPG or L/100km varies with driving style, terrain, speed, air conditioning use and vehicle load — highway cruising is typically more efficient than stop-and-go city driving. Use your vehicle's actual observed efficiency (from the Gas Mileage Calculator) rather than the manufacturer-quoted figure for a more accurate estimate.
Where can I find my car's fuel efficiency?
The window sticker or manufacturer specifications give an official rating, but your actual mileage is usually a bit different — track it yourself with the Gas Mileage Calculator by noting the distance driven and fuel added at your next few fill-ups.
Formula and content last reviewed on .
Results are estimates for information only, not professional advice.
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