How to Calculate Fuel Cost for a Road Trip (Formula + Example)
A road-trip fuel budget is easy to estimate once you know three numbers: the distance, your vehicle’s fuel economy and the price per litre or gallon. The key is to keep the units consistent.
Quick formula: fuel cost = distance × fuel consumption × fuel price. For a metric vehicle that reports litres per 100 km, use: (distance in km ÷ 100) × litres per 100 km × price per litre.
Fuel cost formula for kilometres and litres
Use this formula when your vehicle’s fuel economy is shown as L/100 km:
Fuel cost = (distance ÷ 100) × fuel economy × price per litre
- Distance: the total kilometres you plan to drive.
- Fuel economy: your vehicle’s consumption in litres per 100 km.
- Fuel price: the expected price per litre.
Use the car’s real-world fuel economy if possible. The figure in a brochure may be measured under test conditions and can differ from what you get with traffic, hills, weather, passengers or a loaded boot.
Worked example: a 1,200 km road trip
Suppose the trip is 1,200 km, the car uses 7.5 L/100 km and fuel costs $1.85 per litre.
- Calculate fuel needed: (1,200 ÷ 100) × 7.5 = 90 litres.
- Calculate the fuel cost: 90 × $1.85 = $166.50.
The estimated one-way fuel cost is $166.50. A 2,400 km return trip with the same assumptions would need about 180 litres and cost $333.00.
Check your result with the Fuel Cost Calculator.
How to calculate fuel cost using miles and MPG
If your vehicle uses miles per gallon (MPG), calculate gallons first:
Fuel cost = (distance in miles ÷ MPG) × price per gallon
For example, a 400-mile trip in a car rated at 30 MPG with fuel at $3.50 per gallon requires:
(400 ÷ 30) × $3.50 = $46.67 approximately.
Do not mix kilometres with MPG or litres with a price per gallon. Convert the distance, economy and fuel price first, or use the Fuel Economy (MPG) Calculator.
Allow for detours, traffic and a fuel reserve
Map distances are estimates. Add a realistic allowance for local driving, missed turns, sightseeing and detours. For example, adding 10% to the 1,200 km example gives 1,320 km:
(1,320 ÷ 100) × 7.5 × $1.85 = $183.15.
This is a planning allowance, not a rule. A heavily loaded vehicle, strong headwind, mountain roads, towing or long periods of idling may increase actual consumption. It is also sensible to keep a cash buffer because fuel prices can vary between towns and highways.
Compare two vehicles before you travel
Fuel economy makes a measurable difference. At 1,200 km and $1.85 per litre:
- A car using 7.5 L/100 km costs about $166.50.
- A car using 9.0 L/100 km costs about $199.80.
The more efficient car saves about $33.30 on this one-way trip. For a return trip, the difference would be about $66.60. The Fuel Savings Calculator can help compare the effect of different fuel economies or prices.
What your fuel estimate does not include
Fuel cost is only one part of a road-trip budget. Add tolls, parking, servicing, tyres, meals, accommodation and vehicle depreciation separately. If you are comparing a price change rather than estimating the trip, the percentage guide explains how to calculate the increase between two amounts.
How to improve your estimate
- Use the total route distance, including the return journey.
- Use a recent fuel-economy reading from your own driving.
- Check fuel prices at likely stops instead of using only the cheapest price.
- Round up slightly so a small detour does not break the budget.
- Recalculate if you change the vehicle, route or fuel type.
Frequently asked questions
How much fuel will my trip use?
Multiply the distance in kilometres by the vehicle’s litres per 100 km, then divide by 100. For miles and MPG, divide miles by MPG to get gallons.
Should I calculate one-way or return fuel cost?
Use the full distance you expect to drive. Double a one-way estimate only when the return route and driving conditions are similar.
Why is my actual fuel cost different?
Fuel price, traffic, speed, hills, weather, tyre pressure, passengers and cargo can all change consumption. Treat the result as a planning estimate, then add a sensible buffer.
For a fast estimate, enter your route distance, vehicle efficiency and expected fuel price in the Fuel Cost Calculator before you set off.