How to estimate fuel costs before you leave
A three-number formula and how to use it in the planner.
By CampingSpirit Editors · July 1, 2026 · 3 min read
Fuel is usually the biggest variable cost of a road trip, and it is easy to estimate before you leave. You need three numbers: the distance, your vehicle's real-world consumption and a typical fuel price along the route. Ten minutes of arithmetic gives you a budget that is rarely more than 10 to 15 percent off.
The formula
In miles: divide the distance by miles per gallon, then multiply by the price per gallon. A 1,200-mile trip in a car that gets 30 mpg, with gas at $3.50, costs about $140; a motorhome at 9 mpg would spend about $467 on the same trip. In kilometres: multiply the distance by the consumption in litres per 100 km, divide by 100 and multiply by the price per litre. A 2,000 km trip at 7 l/100 km and €1.80 per litre costs about €252; a motorhome using 12 l/100 km would need about €432.
Be honest about consumption
Official consumption figures assume gentle driving in ideal conditions. Mountain passes, headwinds, motorway speeds, air conditioning, a loaded roof box, bikes on the back or a trailer can raise consumption by 20 to 40 percent. Motorhomes are especially sensitive to speed: driving at 90 instead of 110 km/h often saves more fuel than any other change. Use your own logged average from a similar trip if you have one, and add 10 percent for the unknown.
Prices vary more than you think
In the US, gas in California or near national parks can cost a dollar or more per gallon above the price in Texas or Oklahoma. In Europe, prices differ noticeably between neighbouring countries, and motorway service areas are almost always the most expensive place to fill up. Filling the tank in the cheaper country before a border, or a few kilometres off the motorway at a supermarket station, adds up on a long trip. Remote stretches change the priority: there, the rule is to fill up whenever the tank is half empty.
Electric vehicles
The same formula works with kilowatt-hours: distance times consumption in kWh per 100 km, divided by 100, times the price per kWh. The spread is wider than with fuel, because home charging, slow public chargers and motorway fast chargers can differ by a factor of three or more. Estimate the share of fast charging on your route and price that part separately.
In the planner
Add your vehicle in Account → Vehicles with its real consumption. The trip's Details tab then works out fuel or charging for every leg and for the whole trip, using the prices from your preferences, which you can set separately for the US and for Europe. Change the vehicle and the totals update at once, which makes it easy to compare a car with a campervan before you book.
