Road Trip Gas Calculator

Plan the fuel budget for a road trip. Enter the distance, your car’s fuel economy and the fuel price, and the calculator shows how much fuel you will use, what it will cost one way or return, the cost per person and roughly how many fill-ups you will need based on your tank size. Switch between miles and gallons or kilometres and litres.

How the road trip calculator works

Fuel cost is distance divided by fuel economy, times the price of fuel. In US units, a 420-mile trip in a car that averages 28 mpg uses 15 gallons one way; at $3.50 a gallon that is $52.50. The calculator doubles the distance for a round trip, adds any driving you plan to do at the destination, applies an optional allowance for a heavily loaded car, a roof box, towing or mountain roads, then splits the total between the people sharing the cost. It also estimates your range on a full tank so you can see how many fuel stops to plan.

Finding your real fuel economy

• Check your car’s trip computer for average fuel economy over recent driving.
• Or measure it: fill the tank, reset the trip meter, drive normally, fill up again and divide the distance by the fuel added.
• Official ratings (such as EPA estimates in the US) are a good starting point; highway figures suit long road trips.
• Expect lower economy at high speeds — fuel use rises noticeably above about 60–65 mph (100–105 km/h) for most cars.
• Air conditioning, roof racks and heavy loads all reduce economy.

Fuel economy conversions

UK miles per gallon uses the larger imperial gallon, so the same car shows a higher mpg figure in the UK than in the US.

Worked example

Three friends drive 420 miles each way to a national park, plus about 40 miles of driving around the park, in a car that averages 28 mpg on the highway. With a roof box (+10%), the 880-mile total uses about 34.6 gallons. At $3.50 a gallon the fuel costs about $121, or about $40 each. The 14-gallon tank gives a range of roughly 356 miles when loaded, so refuelling at about 20% left means planning around three fill-ups over the whole trip.

Saving fuel on a road trip

• Drive at a steady speed and use cruise control on flat highways.
• Keep tyres at the recommended pressure — check when cold, including before the trip.
• Remove roof boxes and racks when not needed.
• Pack lighter; every extra 100 lb (45 kg) reduces economy slightly.
• Plan fuel stops where prices are lower; prices near motorways and remote areas are often higher.
• Avoid long idling; turn the engine off during long stops.

Planning fuel stops

On remote routes — deserts, mountain passes, national parks — fuel stations can be far apart. Plan to refuel before the tank drops below about a quarter, and check opening hours for small-town stations, which may close at night. Carry water, a phone charger and an offline map. For electric vehicles, plan charging stops with a dedicated charging map instead, since range and charging times work differently.

Splitting costs fairly

Splitting fuel equally between passengers is the simplest approach. Some groups also split tolls and parking, or reduce the driver’s share since they provide the car and bear wear and tear. Another approach is to use a per-mile rate that includes running costs; tax authorities publish mileage rates for business use, which include much more than fuel.

Tolls, parking and other trip costs

Fuel is often the biggest variable cost of a road trip, but tolls, parking, ferries and park entry fees can add a surprising amount. Toll roads and bridges vary widely by region; route planners usually show which roads charge tolls and let you avoid them, at the cost of extra time and sometimes extra fuel. Hotels in city centres often charge for parking. Adding these to the paid budget workbook gives a complete per-person figure.

Hybrid and electric cars

For hybrids, enter the average mpg you actually achieve on the highway. For electric vehicles, use an energy equivalent: kWh per 100 miles or km and the price per kWh at chargers — for example, 30 kWh per 100 miles at $0.40/kWh is $0.12 per mile. Enter kWh/100 km in the L/100 km field and the price per kWh in the price field for a quick estimate in metric mode.

Privacy

The calculator runs in your browser and stores nothing.