Fuel, Tolls and Distances: Practical US Driving Math for Motorhome and Camper Travelers

Fuel in the United States is sold by the US gallon, roads are measured in miles, and speed limits are posted in miles per hour. A US gallon is 3.785 liters, noticeably smaller than the imperial gallon used in the UK, and a mile is about 1.61 kilometers. Once these two conversions are second nature, most questions about range, cost and daily distance turn into simple arithmetic.

The less obvious parts are practical: how to pay at a pump that expects a US ZIP code, why a toll road may have no booth at all, and how far apart stations can be in the interior West. Prices below are national averages published by AAA on 2 October 2026 and will have moved by the time of travel.

Gallons, miles and the math

Fuel economy is quoted in miles per gallon (mpg), where higher is better, the reverse of liters per 100 km. To convert, divide 235 by the mpg figure: 20 mpg is about 11.8 L/100 km, 15 mpg about 15.7 and 10 mpg about 23.5. A 300-mile day is roughly 480 km. Cost follows from three numbers: miles, mpg and price per gallon. At the AAA national average for regular of $4.40 per gallon (about $1.16 per liter) on 2 October 2026, 300 miles at 10 mpg means 30 gallons and roughly $130.

Consumption in a camper varies widely with size, speed and wind. Large motorhomes commonly return single-digit to low-teens mpg, vans built on a car-based chassis do better, and towing or driving into a headwind at 75 mph raises the figure noticeably. The official EPA ratings on fueleconomy.gov cover only vehicles up to 8,500 lb (3,855 kg) gross weight, so most motorhomes have no rating at all. The practical method is to log the first two or three fill-ups and use that real number.

Grades, diesel and where to buy it

Gasoline comes in three grades labeled by octane: regular at 87, midgrade at 88 to 90 and premium at 91 to 94. The US method gives lower numbers than the RON figures printed on European pumps. On 2 October 2026 AAA listed national averages of $4.40 for regular, $4.92 for midgrade and $5.31 for premium. Many gasoline motorhomes and vans are specified for regular, but the owner’s manual or the label by the filler cap decides. Some high-elevation areas sell 85-octane fuel; unless the engine is an old carbureted one, use the manufacturer’s recommended grade.

Diesel is a different market. It averaged $6.37 per gallon on the same date, well above gasoline, and not every station sells it. Many truck stops along the interstates, including the Pilot Flying J and Love’s chains, have separate diesel lanes with high-flow nozzles and room for long vehicles. Small-town and city stations may have none. Check the pump label before filling, and confirm in a rental which fuel the vehicle takes. Canopies at some urban stations are low, so look for the posted clearance before pulling in with a tall vehicle.

Paying at the pump

Many pumps ask for a five-digit ZIP code before authorizing a card, which a card issued abroad cannot supply. Common workarounds, none of them guaranteed: enter the digits of the home postal code and pad with zeros to five, use the contactless reader with a phone wallet, or run a debit card as credit if the terminal asks for a US PIN. If the pump still declines, the reliable option is to pay inside: give the cashier the pump number and an amount, fill up, and keep the receipt showing the gallons.

Some details differ from Europe. Payment usually comes before or at the start of pumping, and a pre-authorization hold can sit on the card for a few days even when the final charge is lower. Ask the bank to allow international transactions before departure. Rental campers are normally returned with a full tank, and the company may ask for proof of the last fill, so receipts are worth keeping.

Tolls without booths

Toll roads are concentrated in the Northeast, the Midwest, Florida, Texas and around large cities elsewhere; much of the interstate system in the West is free. A growing number are cashless: they bill a transponder (E-ZPass in the Northeast and Midwest, other regional systems such as SunPass in Florida) or photograph the plate and mail a bill to the registered owner. For a visitor in a rental, that owner is the rental company.

Rental companies pass these tolls on with added charges. An analysis by the New York City comptroller of E-ZPass programs found daily convenience fees of $3.95 to $21.49 at ten of eleven companies, charged whether or not the transponder was used, and some billed the higher cash rate. The figures are an illustration of how much policies differ. At pickup, ask what the toll program costs per day, whether the fee is capped on long rentals, and whether it can be declined. Setting the navigation app to avoid tolls often costs only a few minutes.

Long gaps in the West

East of the Mississippi a station is rarely more than a few miles away. In the interior West, across Nevada, Utah, Wyoming, Montana and the desert Southwest, towns can be 50 miles (80 km) or more apart. On routes such as US 50 across central Nevada, nicknamed the Loneliest Road in America, services are sparse and some close early. A workable rule is to refuel at half a tank whenever the next town is uncertain, and never to start a long empty stretch below that. Fuel in remote places is usually dearer than the national average, and mountain grades and altitude raise consumption.

Planning figures

A daily budget of 250 to 300 miles (400 to 480 km) is comfortable in a motorhome once stops and slower two-lane roads are included. Rural interstates are often posted at 65 to 80 mph (105 to 130 km/h), but many drivers find 60 to 65 mph more comfortable in a heavy vehicle. At 10 mpg that is 25 to 30 gallons a day, so a week of driving needs roughly 175 to 210 gallons (660 to 800 liters). Convert the planned miles, divide by a realistic mpg, multiply by the current price on the AAA site and add a margin of 10 to 15 percent. Before the first day, read the rental company’s toll policy and carry two payment cards, one of them with a working PIN.

Sources

• AAA Gas Prices: national average (AAA)
• Octane Ratings in the United States (U.S. Department of Energy, fueleconomy.gov)
• Fuel Economy Information, FAQ (U.S. Department of Energy, fueleconomy.gov)
• Fast Fees: An Analysis of E-Z Pass Fees at Rental Car Companies in NYC (NYC Comptroller)
• Paying at U.S. Gas Pumps with a Foreign Card: ZIP Code Tips (Hola Car Rentals)