How to Calculate Road Trip Fuel Cost
Calculating road trip fuel cost is straightforward when you know three things: how far you are driving, how efficiently your vehicle uses fuel, and what fuel costs at the pump. The formula differs slightly depending on which unit system you use.
Imperial (miles and gallons): Divide your total distance in miles by your vehicle's fuel economy in miles per gallon (MPG). This gives you total gallons used. Multiply that by the price per gallon to get your total fuel cost.
Metric (kilometres and litres): Divide your fuel consumption rate in litres per 100 kilometres (L/100km) by 100, then multiply by your trip distance in kilometres. This gives litres used. Multiply by the price per litre.
For example: a 600 km trip in a vehicle using 8 L/100km at $1.85/litre costs (8 ÷ 100) × 600 × $1.85 = $88.80 in fuel.
Factors That Affect Road Trip Fuel Cost
Vehicle Fuel Economy
Your vehicle's rated fuel economy is measured under controlled conditions and rarely matches real-world driving. Expect 10–20% lower efficiency than the official rating in real road trip conditions, particularly at highway speeds above 65 mph (105 km/h), in mountainous terrain, or in extreme temperatures. Sedan and hatchback drivers typically see figures close to the rated MPG on flat highway routes at legal speeds.
Driving Speed
Aerodynamic drag increases exponentially with speed. At 75 mph versus 55 mph, a typical vehicle consumes 15–25% more fuel per mile. For a 500-mile trip at 30 MPG ($3.50/gallon), slowing from 75 mph to 65 mph can save $5–$8 in fuel and takes only 12–15 extra minutes for every 100 miles of highway driving.
Cargo and Passengers
Every 100 lbs (45 kg) of extra weight reduces fuel economy by approximately 1–2%. A fully loaded family SUV with luggage and passengers can return 10–15% less than its rated highway MPG. Remove unnecessary cargo from your vehicle before a long trip to trim costs.
Terrain and Climate
Mountain driving, stop-and-go traffic, and extreme temperatures all reduce fuel economy. Air conditioning in hot weather typically reduces MPG by 5–25% depending on conditions. Cold temperatures below 0°C (32°F) can reduce fuel economy by 15–24% for short trips until the engine reaches operating temperature.
Fuel Price by Country (2025 Reference)
- Australia: AUD $1.70–$2.10 per litre for unleaded 91 (varies significantly by region)
- United States: USD $3.00–$4.00 per gallon for regular unleaded (state-dependent)
- United Kingdom: GBP £1.40–£1.60 per litre
- Canada: CAD $1.60–$2.00 per litre (higher in BC and Yukon)
- New Zealand: NZD $2.50–$3.00 per litre
- Germany: EUR €1.60–€1.90 per litre
Tips to Reduce Road Trip Fuel Costs
- Inflate tyres to the correct pressure. Under-inflated tyres increase rolling resistance and reduce fuel economy by up to 3%. Check pressure at the start of every long trip when tyres are cold.
- Drive at constant speeds. Use cruise control on motorways to maintain steady speed and avoid the fuel-wasting cycle of acceleration and braking. Cruise control can improve highway fuel economy by 7–14%.
- Plan fuel stops strategically. Use apps like GasBuddy or PetrolSpy to find cheaper fuel along your route. Fuel prices vary by up to 20–30% between stations even in the same city.
- Avoid peak traffic times. Stop-and-go traffic is extremely fuel-inefficient. Idling for 10 minutes burns approximately 0.1–0.2 gallons (0.4–0.7 litres) of fuel with zero forward progress.
- Reduce aerodynamic drag. Remove roof racks and cargo carriers when not in use — even an empty roof rack increases drag and reduces fuel economy by 2–8% at highway speeds.