Fuel Cost Calculator for a Trip
This calculator estimates what a trip will cost in fuel: the total, the cost per person if you are splitting it, and the cost per mile or kilometer. Enter the distance, your vehicle's fuel efficiency and the local fuel price, in US units (miles, mpg, per-gallon prices) or metric (kilometers, liters per 100 km, per-liter prices).
It answers the questions that come up before every road trip: is driving cheaper than flying, what is a fair split between friends, and what does the daily commute cost per week?
The fuel cost formulas
US units: Fuel needed = Distance ÷ MPG, then Cost = Gallons × Price per gallon
Metric: Fuel needed = Distance × (L/100km) ÷ 100, then Cost = Liters × Price per liter
The two efficiency conventions run in opposite directions: higher mpg is better, while lower L/100 km is better. To convert: L/100 km = 235.2 ÷ mpg (US). A 30 mpg car uses about 7.8 L/100 km.
Worked example
A 250-mile one-way trip in a car averaging 30 mpg, with gas at $3.50/gallon, four friends sharing:
| Fuel needed | 250 ÷ 30 = 8.3 gallons |
|---|---|
| Total cost | 8.3 × $3.50 = $29.17 |
| Round trip | $58.33 |
| Per person (round trip) | $14.58 |
| Cost per mile | $0.117 |
Four people, five hundred miles, under $15 each. Fuel is not the whole cost of driving, though. Tires, servicing and depreciation typically add several times the fuel cost per mile.
Getting your real-world efficiency right
The advertised fuel economy figure comes from lab conditions. Real driving usually lands 10–20% worse, and worse still at highway speeds above 70 mph, with roof boxes, heavy loads, or stop-and-go traffic. The most accurate input is your own measured figure: fill the tank, reset the trip meter, drive normally, refill, and divide miles by gallons. Most recent cars also show a running average that is close enough for planning.
For a fair carpool split, many groups add 10–15% over pure fuel cost for wear and tear. That is still far below official mileage-reimbursement rates, which price in the full cost of running a car.
Frequently asked questions
How do I calculate fuel cost per mile?
Divide the fuel price by your mpg. At $3.50 per gallon and 30 mpg, fuel costs about 11.7 cents per mile. A 12,000-mile driving year at that rate is roughly $1,400 of fuel.
How much does it cost to drive 1,000 miles?
At 30 mpg and $3.50 per gallon: 1,000 ÷ 30 = 33.3 gallons, about $117. A 20 mpg vehicle costs $175 for the same trip. Vehicle choice moves long-trip costs more than pump-price shopping does.
Should we split fuel cost equally including the driver?
The usual convention is to split the fuel across everyone in the car, driver included, since the driver already contributes the vehicle and its wear. For regular commute carpools, adding a modest wear-and-tear margin on top of fuel is common and fair.
How do mpg and L/100 km relate?
L/100 km = 235.2 ÷ mpg (US gallons). So 25 mpg is about 9.4 L/100 km, and 40 mpg is about 5.9 L/100 km. UK gallons are larger, so UK mpg figures read about 20% higher than US ones for the same car.
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This calculator is for general information and education only. It is not professional advice. Confirm important decisions with a qualified adviser.