Trip & budget
How to budget fuel for a road trip
A road-trip fuel budget is a distance estimate plus a fuel-use estimate plus a price estimate. The hard part is not the arithmetic. It is being honest about detours, load, speed and the price you will actually pay.
Quick answer
Add up the total route distance, divide by your expected MPG, multiply by the price per unit, then add a buffer for detours and conditions. Convert units before crossing borders.
Key takeaways
- Start with total distance, not one tank.
- Use a realistic loaded-trip MPG.
- Add a buffer and keep a currency/unit note.
Estimate the route distance
Use the driving distance, not the straight-line distance. Add planned detours and a little extra for finding parking or missing a turn. If you are returning home, include the return leg.
Choose a trip MPG
A fully loaded car with passengers, luggage and a roof box will not match a solo highway test. Use a conservative figure. If you have measured the car on a similar trip before, use that number.
For a mixed route, city and highway consumption can differ enough that a single optimistic figure is misleading.
fuel used = total distance ÷ trip MPG fuel cost = fuel used × price per unit budget = fuel cost × 1.10 to 1.15
Crossing borders
If the trip crosses from miles to kilometres, or from gallons to litres, convert the distance and price into one system before multiplying. A spreadsheet with a unit column is safer than doing it in your head at a fuel stop.
The calculator can handle each leg separately. Add the results in a common currency if you need one total.
Questions
How much should I budget for fuel?
Should I use highway MPG?
How do I handle multiple currencies?
Sources
- GOV.UK — weekly road fuel prices — UK price statistics for context, not a live station price.
- US EIA — gasoline and diesel prices — US regional and national averages.
- European Commission — Weekly Oil Bulletin — EU fuel price monitoring.
- fueleconomy.gov — US fuel-economy ratings — EPA label values, test-cycle context and consumer guidance.
Try the calculator
Related guides
Round-trip fuel cost formula
A simple method for round-trip fuel estimates, including detours, unit changes and the difference between one-way and return distance.
How much fuel does 100 miles use? A simple guide
Work out fuel use and fuel cost for 100 miles in UK or US units, with example tables and the formula behind the answer.
Do roof boxes and roof racks increase fuel use?
Why roof accessories add drag, how speed makes the effect worse, and how to measure the real cost on your own car.
A note on prices and rules
Page last reviewed: . Formulas are covered by automated tests. Prices are inputs, not live data.