Estimate road-trip fuel spending from distance, MPG and gas price.
Calculator
Trip Budget
Cost Comparison
Trip Calculation Details
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How to calculate fuel cost for a trip
Enter the one-way route distance, choose one way or round trip, and enter how many identical trips you expect to make. Then add a realistic fuel-economy value and the pump price. Distance, fuel economy, and price units are independent, so a route in kilometers can be combined with US MPG and a price per liter without manual conversion.
total route distance = one-way distance x trip direction multiplier x number of trips + extra detour distance
US fuel needed = total miles / US MPG
fuel cost = fuel needed in the selected price unit x price per unit
Road-trip fuel cost example
A 650-mile one-way trip in a vehicle averaging 28 US MPG requires about 23.21 US gallons. At $3.60 per US gallon, the fuel-only estimate is $83.57. A 10% fuel buffer raises the planned fuel budget to $91.93. If two travelers split that budget evenly and there are no other shared costs, each person's share is about $45.96. Selecting round trip doubles the base route before any detour distance is added.
What the results include
The calculator separates estimated fuel cost from the planning buffer and other shared trip costs. Fuel cost is the direct result of distance, efficiency, fuel volume, and pump price. The fuel budget adds the percentage buffer. The total trip budget then adds any tolls, parking, ferry charges, or other shared costs entered under More trip budget options. Maintenance, depreciation, lodging, meals, and personal expenses remain outside the estimate unless you deliberately include them in the shared-cost field.
Choose a realistic MPG or L/100 km value
For a future road trip, a recent fill-to-fill result from similar highway and load conditions is often more useful than a best-case dashboard reading. Use the MPG calculator to measure a tank from odometer readings and refill volume. If no measured value is available, find the combined or highway rating for the exact vehicle configuration in the official FuelEconomy.gov vehicle comparison, then consider whether speed, weather, elevation, cargo, towing, traffic, or idling may make the real trip less efficient.
US MPG, Imperial MPG, km/L, and L/100 km
US MPG and Imperial MPG use different gallon sizes, so the numbers are not interchangeable. For the same physical efficiency, Imperial MPG is about 20% higher. Kilometers per liter is a distance-per-volume measure, where higher is better. Liters per 100 kilometers is a consumption measure, where lower is better. The calculator converts every option to a shared US-gallon and mile basis before calculating cost, then reports gallons and liters together.
L/100 km = 235.214583 / US MPG
Imperial MPG = US MPG x 1.2009499
Unit conversions use 1 mile = 1.609344 kilometers, 1 US liquid gallon = 3.785411784 liters, and 1 Imperial gallon = 4.54609 liters. The NIST conversion tables distinguish the two gallons. A price per Imperial gallon must therefore be applied to Imperial gallons, not the US-gallon total.
Fuel price units and currency
Select whether the entered price applies to a US gallon, Imperial gallon, or liter. The calculator applies that price to the matching converted fuel volume. The currency menu changes the symbol and formatting only; it does not retrieve live fuel prices or exchange rates. For a multi-state or cross-country trip, use a weighted average of expected pump prices rather than the cheapest price at the starting point.
Extra distance and a fuel budget buffer
Map routes rarely capture every mile. Local driving, food and fuel stops, hotel access, missed exits, and planned side trips can add distance. Enter those miles or kilometers once in the detour field; they are added after the trip-direction and repeat-trip multipliers. The percentage buffer is then applied to calculated fuel cost, which gives a transparent cushion without pretending the car will consume a fixed extra number of gallons.
The US Department of Energy notes that route choice, vehicle selection, driving behavior, and real operating conditions can materially change fuel use. Its road-trip vehicle comparison demonstrates how different vehicles can produce very different fuel costs on the same route.
Split gas money fairly
The per-person figure divides the total trip budget evenly by the number of people entered. That is useful when everyone agrees to share fuel, buffer, tolls, and parking equally. It does not compensate the vehicle owner for wear, depreciation, or insurance. If the driver is not expected to pay, enter only the paying passengers as the split count, or use the displayed total to agree on a custom arrangement.
Repeated round trips with a detour
Two round trips with a 650-mile one-way route and 40 extra miles across the whole plan cover 650 x 2 x 2 + 40 = 2,640 miles. At 28 US MPG and $3.60 per US gallon, fuel costs about $339.43. With a 10% buffer and no other costs, the budget is $373.37, or $93.34 each for four paying travelers. The 40-mile detour is added once, not once per direction or repeated trip. Costs are calculated before display rounding.
How to improve the estimate
- Use the route distance from the actual planned start and destination, not city-center approximations.
- Select round trip only when the return distance is reasonably similar.
- Use measured fuel economy from comparable driving or the exact vehicle's official rating.
- Enter a realistic average fuel price for the whole route.
- Add detours separately and use the buffer for uncertainty rather than silently inflating MPG or distance.
- Recalculate if the vehicle, trailer, passenger load, route, or fuel price changes.
Frequently asked questions
Should I enter one-way or total distance?
Enter the one-way route distance, then choose One way or Round trip. The calculator applies the selected multiplier and displays total distance so you can verify the interpretation.
Can I use kilometers with US MPG?
Yes. Distance, efficiency, and fuel-price units are converted independently.
Does the calculation include idling?
Only when your entered real-world fuel economy already reflects comparable idling. Use the fuel buffer when traffic or stationary running is uncertain.
Does it include tolls and parking?
Not in the fuel-only result. Add them under More trip budget options to include them in the total and per-person budget.
Can I use the result for an electric vehicle?
No. This calculator models liquid fuel by volume. Electric vehicles require energy consumption in kWh per distance and an electricity price per kWh.