A 17-hour drive uses 57 to 85 gallons of gas, depending on your car's fuel economy

The amount of gas you need depends almost entirely on how many miles per gallon your vehicle gets. A car that averages 25 mpg will burn roughly 57 gallons over 1,425 miles (the distance covered in 17 hours at 84 mph average). A truck or SUV averaging 18 mpg will use about 79 gallons. A hybrid or efficient sedan at 35 mpg might use only 41 gallons. Check your vehicle's fuel economy on the window sticker if you bought it recently, or look it up on fueleconomy.gov by year, make, and model.

Real-world fuel economy is usually lower than the EPA estimate, especially on long highway drives. Factors like tire pressure, engine condition, cargo weight, and driving speed all affect how much gas you actually burn. A car rated at 28 mpg highway might get 24 mpg in practice if your tires are underinflated or you're carrying extra weight.

Key Takeaways

  • Most cars need 50 to 80 gallons for a 17-hour highway trip, but this varies based on your vehicle's fuel economy and real-world conditions.
  • You can find your car's fuel economy on fueleconomy.gov or by checking the window sticker from when it was sold.
  • Plan to stop for gas every 300 to 400 miles rather than trying to run on a single tank, since most cars hold 12 to 16 gallons.
  • Keeping tires properly inflated and avoiding excessive speed will reduce fuel consumption on a long drive.
  • Budget $75 to $140 for fuel costs at current gas prices, depending on your region and vehicle type.

How to calculate gas needed for your specific vehicle

Start with your car's highway fuel economy rating. This is the number you'll see on the yellow EPA label on new cars, or you can search fueleconomy.gov for your year, make, and model. Highway ratings are more accurate for long drives than city ratings because highway driving involves fewer stops and more consistent speeds.

Divide the total miles by your fuel economy. For a 1,425-mile trip (17 hours at 84 mph average), divide 1,425 by your mpg. A car rated at 25 mpg highway needs 57 gallons. A truck at 18 mpg needs 79 gallons. A hybrid at 35 mpg needs 41 gallons. This gives you the theoretical amount needed if you started with a full tank and drove straight through.

Add a safety margin of 10 percent. This accounts for traffic, detours, and the fact that your actual fuel economy may be lower than the EPA estimate. For the 25 mpg car, that's 57 × 1.1 = 63 gallons total.

Why you can't rely on a single tank of gas

Most passenger cars hold between 12 and 16 gallons. A truck or SUV might hold 20 to 26 gallons. Even a large sedan with a 16-gallon tank and 25 mpg highway rating can only go about 400 miles before the fuel warning light comes on. A 17-hour drive covers 1,425 miles, so you'll need to refuel at least three or four times.

Plan your stops in advance using a mapping app. Google Maps and Apple Maps both show gas stations along your route. Aim to refuel when your tank drops to one-quarter full rather than waiting until the warning light comes on. This prevents the risk of running out of gas between stations in rural areas, where gas stations can be 50+ miles apart.

How driving speed affects fuel consumption

Fuel economy drops significantly above 50 mph. Most cars are most efficient between 45 and 55 mph. For every 5 mph you drive above 50 mph, fuel economy decreases by roughly 7 percent. A car rated at 28 mpg at 55 mph might only get 24 mpg at 70 mph.

On a 17-hour drive, the difference between averaging 65 mph and 75 mph can add 5 to 10 gallons to your fuel consumption. If you're trying to minimize gas costs, driving at a steady 60 to 65 mph will save money even if it adds an hour to your trip time.

Factors that reduce fuel economy on long drives

Underinflated tires are the single biggest culprit. Check your tire pressure before a long drive — you'll find the correct pressure on a sticker inside the driver's door, not on the tire itself. Tires lose 1 psi for every 10-degree drop in temperature, so a cold morning departure can mean your tires are 3 to 5 psi below spec.

Roof racks, cargo carriers, and extra weight all increase fuel consumption. A roof rack alone can reduce fuel economy by 5 percent. Carrying an extra 100 pounds reduces it by another 1 to 2 percent. If you're packing for a long trip, pack light and keep cargo inside the car rather than on top.

Air conditioning use increases fuel consumption by 3 to 10 percent depending on how hard the system is working. On a long highway drive in summer, the fuel cost of running AC is usually worth the comfort, but it's worth knowing it's not free.

Estimating fuel costs for your trip

Multiply your total gallons needed by the current average gas price in your region. Gas prices vary by state and change weekly. As of early 2024, prices range from roughly $2.80 to $3.50 per gallon depending on location, though this changes frequently.

For a 25 mpg car needing 63 gallons at $3.20 per gallon, expect to spend about $200 on fuel. A truck needing 87 gallons at the same price would cost $278. A hybrid needing 47 gallons would cost $150. These are estimates — actual costs depend on where you refuel and current prices along your route.

Use GasBuddy or your mapping app to find the cheapest stations along your route. Prices can vary by 20 to 40 cents per gallon between nearby towns, so planning refueling stops at cheaper stations can save $10 to $20 over a long drive.

Frequently Asked Questions

What if I don't know my car's fuel economy?

Go to fueleconomy.gov and search by year, make, and model. You'll see both EPA estimates and real-world data from other drivers. If your car is older or not in the database, check your owner's manual or calculate it yourself: fill your tank, drive until you refuel, note the miles driven and gallons added, then divide miles by gallons.

Should I fill up before starting a long drive?

Yes, start with a full tank. This gives you the maximum range before your first refueling stop and reduces the number of stops you need to make. It also means you're not starting with an unknown amount of fuel.

Is it cheaper to drive slower to save gas?

Usually yes, but the time cost matters. Driving 60 mph instead of 75 mph might save 8 to 10 gallons on a 1,425-mile trip, worth roughly $25 to $35. But it adds 3 to 4 hours to your drive time. Whether that trade-off makes sense depends on your schedule and how much you value your time.

What's the best time to refuel on a long drive?

Refuel when your tank reaches one-quarter full, not when the warning light comes on. This prevents running out of gas in areas with sparse stations. On a 17-hour drive, you'll likely refuel every 3 to 4 hours, which also gives you natural breaks to rest and stretch.

Do electric vehicles use less money for long drives?

Yes, but charging takes longer than refueling. An electric car might cost $8 to $12 in electricity for the same distance a gas car spends $50 to $80 on fuel. However, charging stations are less common than gas stations in rural areas, and a full charge takes 20 to 45 minutes depending on the charger type. Plan your route carefully using PlugShare or your vehicle's navigation system.