Fuel Cost

Calculating Trip Fuel Cost

A trip’s fuel cost is the distance traveled, divided by your vehicle’s fuel economy, multiplied by the price of fuel. Enter your trip distance, your vehicle’s fuel economy (in MPG or L per 100 km, whichever you know), and the price of fuel, and this calculator returns how much fuel you’ll need and what it will cost.

If you don’t already know your vehicle’s fuel economy, the Gas Mileage (MPG) Calculator figures it out from your last fill-up, and its result carries straight into this calculator.

Key Factors to Consider

• A trip’s driving type affects which fuel economy figure is most accurate. Highway-heavy driving typically achieves better fuel economy than city, stop-and-go driving — use a trip-appropriate figure (or your vehicle’s combined rating) rather than an optimistic best-case number if you want a realistic estimate for a specific trip.
• Speed, driving style, and load all reduce real-world economy below a rated figure. Aggressive acceleration, higher highway speeds (aerodynamic drag rises sharply above roughly 60 mph), a heavily loaded vehicle, or towing all use more fuel per mile than a gentle, unloaded drive at moderate speed.
• Double-check that the distance entered matches the trip you’re actually estimating. A common input mistake is entering a one-way distance when the trip is really a round trip (or vice versa) — the calculator has no way to know your intent, so it computes exactly what’s entered.

The Formula

$$\vC{\text{Fuel Needed (L)}} = \vA{\text{Distance (km)}} \times (\vB{\text{L per 100 km}} \div 100)$$ $$\vE{\text{Total Cost}} = \vC{\text{Fuel Needed}} \times \vD{\text{Price per Liter}}$$ $$\text{Cost per km} = \frac{\vE{\text{Total Cost}}}{\vA{\text{Distance}}}$$

When working in MPG and price-per-gallon instead, this calculator converts internally so the math comes out the same regardless of which unit system you’re more comfortable with.

Worked Example

A 500 km trip in a vehicle getting 8 L per 100 km, with fuel at $1.50 per liter:

1. Fuel Needed: $\vA{500} \times (\vB{8} \div 100) = \vC{40} \text{ liters}$.
2. Total Cost: $\vC{40} \times \vD{1.50} = \vE{60.00}$.
3. Cost per km: $\vE{60.00} \div \vA{500} = 0.12$.

Common Mistakes

• Using a vehicle’s best-case highway rating for a trip that’s mostly city driving. As covered above, driving type meaningfully changes real fuel economy — plugging in an optimistic highway figure for a stop-and-go commute understates how much fuel the trip will actually use.
• Entering an MPG figure into a field expecting L per 100 km, or vice versa. These two figures describe the same efficiency as an inverse relationship, not a simple unit conversion — a more efficient vehicle has a HIGHER MPG number but a LOWER L/100 km number, so swapping one for the other in the wrong field produces a nonsensical result.
• Entering a one-way distance when the trip is actually a round trip. As covered above, the calculator computes exactly what’s entered — doubling the distance for a there-and-back trip (or halving it if only one leg was meant) is a common source of a fuel cost estimate that’s off by exactly 2x.
• Ignoring how a heavy load, roof cargo, or towing lowers real-world fuel economy. As covered above, these all increase drag or weight beyond what a vehicle’s rated fuel economy assumes — using the unloaded rating for a fully packed road trip or one towing a trailer understates the actual fuel needed.

Useful to Know

• For a longer trip with multiple stops or legs, the Road Trip Cost Calculator extends this same math across an entire itinerary rather than a single distance.
• If the vehicle is electric rather than gas- or diesel-powered, the EV Range Calculator answers the equivalent “how far can I go, and what will it cost” question using electricity cost and battery range instead.
• Fuel is only one line item in what a vehicle actually costs to own and run — the Car Ownership Cost Calculator adds in insurance, maintenance, and depreciation for the fuller picture.