Estimating Fuel Costs for a Long Drive, and the Habits That Waste Fuel

Before a holiday drive or a family road trip, it is useful to know roughly how much fuel will cost, especially when several people share the car and plan to split expenses. The calculation is simple; knowing why real costs drift from the estimate makes it far more accurate.

One Formula

Fuel cost = distance ÷ fuel economy × price per liter. Seoul to Busan is about 400 km by expressway. In a car rated at 13 km/L you need 400 ÷ 13 ≈ 30.8 L. At 1,856 won per liter (around the October 2026 national average in Korea) that is about 57,100 won one way, or about 114,200 won for the round trip. Tolls and rest-stop spending come on top.

Rated Economy Is Rarely What You Get

Official figures come from standardized tests. On real roads, traffic jams, air conditioning, passengers and luggage all reduce efficiency, and on heavily congested holiday weekends the gap can be large. For planning, the average economy on your dashboard or your own fill-up records is more realistic. At 10 km/L the same 400 km costs about 74,200 won, roughly 17,000 more than the rated figure suggests.

Habits That Waste Fuel

Hard acceleration is the biggest culprit. Flooring it from every light, or tailgating and then braking and accelerating again, burns fuel quickly; leaving more room to the car ahead cuts much of that waste. Low tire pressure increases rolling resistance, lowers economy and wears tires faster, so check the recommended pressure on the sticker inside the driver's door. Remove luggage you do not need and unused roof boxes. At highway speeds air resistance rises steeply, and cruise control helps keep speed steady.

Air Conditioning or Open Windows?

Air conditioning draws power from the engine, so it costs some fuel. Open windows at highway speed add drag, which can cost more. A common rule of thumb is windows at low speeds and closed windows with moderate air conditioning on the highway. If the car is hot at the start, open the windows briefly to let the hot air out before switching the air conditioning on.

Where to Fill Up

Prices can differ by tens of won, sometimes more than 100 won per liter, between stations in the same area. Korea National Oil Corporation's Opinet service lists station prices along your route. Expressway rest-stop stations are convenient but not always the cheapest, so many drivers fill up in town before leaving. Do not stretch the tank until the warning light comes on to save a little; plan stops with a margin.

Electric and Hybrid Cars

Electric cars use kWh instead of liters. At 5 km/kWh, 400 km needs 80 kWh; at about 347 won per kWh for fast charging, that is roughly 27,800 won. Charger type and membership plans change the price a lot, and cold weather reduces range. Hybrids shine in stop-and-go city traffic and gain less on long highway runs.

Renting a Car Abroad

The US measures economy in miles per gallon and much of Europe in liters per 100 km. One US mpg is about 0.425 km/L, so a 30 mpg car manages about 12.8 km/L. With L/100 km, smaller is better, the opposite of km/L: 7 L/100 km equals 100 ÷ 7 ≈ 14.3 km/L.

Sharing Costs With Passengers

Combine fuel, tolls and parking before splitting. Actual receipts are the most accurate basis, but sharing an estimate before you set off makes the final split easy to agree on. Since the driver also covers wear on the car and does the tiring work, many groups reduce the driver's share.

Pick your car model in the Fuel Cost Calculator to fill in its rated economy automatically, or replace it with your real-world figure for a more realistic estimate.