Core formulas
Required fuel equals total distance divided by fuel economy. Fuel cost equals required fuel multiplied by price per liter. Apply the return-trip multiplier before calculating when the input is one-way distance.
For a shared car, divide the total by travelers to estimate an equal share.
- Fuel required = total distance ÷ real economy
- Fuel cost = fuel required × price per liter
A 200 km example
Driving 200 km at 12 km/L requires about 16.67 L. At 1.70 per liter, the estimated fuel cost is about 28.33 in the same currency scale.
Four equal shares are about 7.08 each, although a group may choose a different arrangement for the driver.
Why real economy matters
City traffic, highway share, weather, cargo, and driving style change actual economy. A recent dashboard average or fill-up record usually reduces error.
For planning, entering a slightly lower economy creates a useful buffer.
Costs outside fuel
Tolls, parking, washing, tires, maintenance, and depreciation are not part of basic fuel cost. Add them separately when comparing the full cost of transportation.
Fuel prices vary by location and discount, so use the price you expect to pay near departure.
Prepare distance, real economy, and price consistently
Use the real round trip plus local driving and likely detours, not only one-way map distance. Recent dashboard or fill-up economy is often more realistic than a published rating. Traffic, motorway share, winter conditions, climate use, and load can change consumption, so test a conservative economy for long trips.
Enter the expected price per litre for the fuel the vehicle actually uses. Apply card or point discounts only when available. For international trips, convert miles, gallons, kilometres, and litres before mixing values.
- Include round trip, local travel, and detours
- Prefer recent real-world economy
- Match fuel type and price units
Core formula and a 320 km example
Fuel required equals distance divided by economy; cost equals fuel required times price. A 320 km round trip at 12.5 km/L needs about 25.6 L. At 1,700 won per litre, the estimate is 43,520 won. Round at the final stage to reduce accumulated error.
At 10 km/L, the same trip needs 32 L and 54,400 won. Compare normal, traffic, and winter cases. Tolls, parking, rental price, and depreciation are not fuel, so add them separately for total trip cost.
- Fuel = distance ÷ economy
- Cost = fuel × price per litre
- Add tolls and parking separately
Use the estimate for group splitting and vehicle choice
Before travel, agree which fuel, toll, and parking items are shared. If the group compensates vehicle provision or driving differently from an equal split, disclose the rule and estimate in advance. Keep the pre-trip estimate distinct from settlement using actual receipts.
For two vehicles, use identical distance and price with each realistic economy. Also consider capacity, toll class, and refuelling convenience. Electric vehicles require kWh price and km/kWh, so do not force them into a litre-based formula.
- Agree the shared-cost scope
- Separate forecasts from receipt settlement
- Compare vehicles under matching trip conditions
Record actual use to improve the next estimate
Record the starting state or fill up, then refill after the trip to compare actual litres. Save distance and consumption by season and route. Averages across several trips are more reliable than one short run affected by idling and pump variation.
When actual cost differs sharply, check missing distance, traffic, idling, tyre pressure, load, price, and unit mistakes. The calculator is a budget estimate, not a diagnosis. Repeated abrupt economy loss should be handled under the vehicle's inspection guidance.
- Record distance and fuel before and after
- Build seasonal and route averages
- Treat persistent efficiency loss as a maintenance question