How the road trip cost is calculated
The calculator turns your trip into three numbers: how much fuel you use, what it costs and how the total is shared. It first finds the miles you will drive (doubling the distance for a round trip), then divides by your fuel economy to get gallons. Gallons times the price per gallon gives the cost of gas. Tolls and parking, which you enter for the whole trip, are added on top, and the total is divided by the number of people sharing the car.
You can work in miles and miles per gallon (mpg), or in kilometers and liters per 100 kilometers (L/100 km). The conversions use the exact NIST factors, and you can switch the units at any time: the numbers you typed are converted, so your trip stays the same. For example, 8 L/100 km is about 29.4 mpg. Results are shown in both unit systems.
Where the gas price comes from
The default price is the most recent weekly average retail price for regular gasoline published by the U.S. Energy Information Administration (EIA), built into the page when it was last updated. The date is shown under the price. You can pick the national average, a region, one of several states or a major city, and you can type any price you like. Prices differ from station to station and from state to state, so treat the default as a starting point. If the average is not available, the price box is left empty for you to fill in.
What affects your real fuel economy
The mpg figure on a car's window sticker is a laboratory estimate. In real life, fuel use rises with high speeds, heavy loads, roof boxes, hills, cold weather and air conditioning, and it falls with steady, moderate driving. The U.S. government's fueleconomy.gov site lists the official rating of most cars sold in the U.S., which is a good number to start with. If you are driving a rental car, ask the company for the fuel type and look up the model.
Costs the calculator leaves out
This tool covers fuel, tolls and parking only. Rental fees, one-way drop-off charges, insurance, lodging, food, tires and general wear on your own car are not included. Rental companies may charge a daily fee for a toll device, so ask at the counter. Many U.S. toll roads are cashless and send a bill by mail or use an electronic pass, so check the toll authority for the states you will cross.
Splitting costs fairly
Enter the number of people sharing the cost, including the driver, and the calculator shows the cost per person. Some groups divide the gas equally and let the driver keep their own parking costs, and others split everything. Decide before you leave so there are no surprises. To plan the rest of your trip, try the travel budget calculator, add tips with the tip calculator, or see this week's prices on the gas prices page.
Frequently asked questions
Where does the default gas price come from?
It is the latest weekly average retail price of regular gasoline from the EIA, saved in the page each time CentDaily updates its data. The date appears below the price box. Prices at the pump change every day, so enter your own price if you know it.
How do I enter fuel economy in L/100 km?
Change the fuel economy unit to "Liters per 100 km." Lower numbers mean a more efficient car. The calculator converts to gallons with the exact factor of 3.785411784 liters per U.S. gallon, so 30 mpg and 7.84 L/100 km give the same result.
Does a round trip double the tolls and parking?
No. The round-trip choice doubles the distance and the fuel. Tolls and parking are the totals you enter for the entire trip, so enter both directions yourself, such as the toll each way.