How to use the road trip fuel stops calculator
- Enter the trip distance, your fuel tank size and your fuel economy.
- Enter the reserve you want to keep in the tank and the fuel you start with as a share of a full tank.
- Open More options to enter a fuel price and see the cost of the fuel.
- Read the number of fuel stops, your usable range per tank and the latest mile marker for each stop.
Formula
Usable range per tank = tank size x (1 - reserve %) x mpg
Range at the start = tank size x (starting fuel % - reserve %) x mpg
Stops = (distance - range at the start) / usable range, rounded up
Fuel used = distance / mpg
The reserve is fuel you plan never to use, so a stop is planned before the tank falls that low. A stop fills the tank completely.
A 900 mile trip in a car with a 14 gallon tank
At 28 mpg with a 15% reserve, each tank gives 14 x 0.85 x 28 = 333.2 miles of usable range. Starting full, you can drive 333.2 miles before the first stop. Then (900 - 333.2) / 333.2 = 1.7, which rounds up to 2 stops. The trip uses 900 / 28 = 32.1 gallons, which is $112.50 at an example price of $3.50 a gallon.
A 300 mile trip needs no stop. A 2,500 mile trip in a 12 gallon, 30 mpg car with a 10% reserve, starting half full, has a starting range of 144 miles and a usable range of 324 miles, and needs 8 stops. A 334.6 mile trip just passes the first range of 333.2 miles and needs 1.
Planning stops in real life
The stops are the latest points to refuel, not the best ones. In practice you stop where there is a station, a meal or a rest break, so plan to refuel a bit before the limit, especially in places where services are far apart. A reserve of 15% on a 14 gallon tank is about 2 gallons, which is a comfortable margin on most roads.
What changes your fuel economy
Speed, headwinds, hills, a loaded trunk, a roof box, cold weather and air conditioning all change the miles you get from a gallon. Use your own highway figure, ideally from a few fill-ups, and consider lowering it for a heavily loaded car. The fuel price is an example, and prices vary along the route.
To measure your real fuel economy use the MPG Calculator, to split the cost use the Fuel Cost Calculator and to budget the whole trip use the Trip Budget Planner.
Assumptions and limits
- Fuel economy is the same for the whole trip, and each stop fills the tank.
- You plan never to use the reserve, and the starting fuel is the share of a full tank you enter.
- The fuel price is an example, and the page uses US units: miles, gallons and miles per gallon.
- Nothing is uploaded. Calculations run in your browser.
Frequently asked questions
Why keep a reserve?
Fuel gauges are not exact, and the next station may be farther than you expect. A reserve means you never plan to arrive on empty. Choose the margin that lets you drive without worry.
How many miles can I go on a tank?
Multiply the tank size by the miles per gallon, then subtract the reserve. The page shows this as the usable range per tank. Real range varies with driving conditions.
What if I start with a partly full tank?
Enter the fuel you start with as a share of a full tank. The range at the start is smaller, and the first stop comes sooner.
Does it work for an electric car?
No. It is built for a fuel tank in gallons and a fuel economy in miles per gallon. Charging stops work differently because charging speed, the share of the battery you charge and the location of chargers all matter, so use your car's own range and charging planner.