Figuring out gas for a trip takes two steps: divide the distance by your car's MPG to get gallons, then multiply gallons by the price per gallon to get the budget. A 480-mile drive in a 25-MPG car is about 19 gallons — roughly $67 at $3.50 a gallon. The gas cost calculator does both steps for any trip; this guide is the planning math around it.
How to figure out gas for a trip
Get the driving distance from your maps app, then divide by your real-world MPG — the window-sticker number minus about 10% is a fair estimate for a loaded car on the interstate (or measure it with the MPG calculator). That quotient is the gallons you'll burn. Multiply by your region's gas price and round up — that's the trip's fuel budget.
How much gas does an 8-hour drive take?
Eight hours of interstate driving with normal stops covers roughly 480 miles at an average of 60 mph. At 25 MPG that's about 19 gallons of gas — a budget of $58–$77 with gas between $3.00 and $4.00 a gallon. A 40-MPG hybrid does the same day on about 12 gallons; a 17-MPG truck or loaded SUV needs 28.
How many gallons — and fill-ups — for 1,000 miles?
A 1,000-mile leg at 25 MPG burns about 40 gallons. Most cars carry a 14–16 gallon tank and you won't want to run it to fumes, so plan on roughly three fill-ups beyond the tank you leave with. Fill up before leaving — home-town gas is usually cheaper than interstate-exit gas — and don't let the gauge fall past a quarter in sparse stretches out west.
Gas needed by trip length
Interstate pace (about 60 mph average including stops), a typical 25-MPG car, gas at $3.50:
| Driving time | Distance | Gallons | Gas budget |
|---|---|---|---|
| 2 hours | ≈120 mi | ≈5 | ≈$17 |
| 4 hours | ≈240 mi | ≈10 | ≈$34 |
| 8 hours | ≈480 mi | ≈19 | ≈$67 |
| 12 hours | ≈720 mi | ≈29 | ≈$101 |
| 2 long days | ≈1,000 mi | ≈40 | ≈$140 |
How far does a gallon get you?
Flip the same math when you're thinking in gallons instead of miles: gallons × MPG = range. Three gallons moves a 25-MPG car about 75 miles; the same three gallons takes a 40-MPG hybrid 120 miles. It's a handy sanity check when the low-fuel light comes on and the next exit sign says 40 miles.
Pad the budget 15%
Real trips beat the estimate: city traffic at each end, detours, headwinds, a cargo box, and A/C in July all pull MPG down, and gas along interstates runs $0.20–$0.40 over the local average. Adding 15% to the calculator's number is the difference between a budget and a guess.