Here's the formula for a road trip's fuel cost:
Gas cost = miles ÷ miles per gallon × price per gallon
A 500-mile trip in a car that gets 25 mpg needs 500 ÷ 25 = 20 gallons. At $3.50 a gallon, that's $70.
Gas cost chart
At $3.50 a gallon:
| Trip distance | 20 mpg | 25 mpg | 30 mpg | 40 mpg |
|---|---|---|---|---|
| 100 miles | $17.50 | $14.00 | $11.67 | $8.75 |
| 250 miles | $43.75 | $35.00 | $29.17 | $21.88 |
| 500 miles | $87.50 | $70.00 | $58.33 | $43.75 |
| 1,000 miles | $175.00 | $140.00 | $116.67 | $87.50 |
| 1,500 miles | $262.50 | $210.00 | $175.00 | $131.25 |
| 2,800 miles | $490.00 | $392.00 | $326.67 | $245.00 |
2,800 miles is roughly a one-way drive between New York and Los Angeles. If gas where you're driving costs more or less than $3.50, scale the numbers: at $4.20 a gallon, costs are 20% higher.
A full example
Four friends drive 640 miles each way, for 1,280 miles in total. Their SUV averages 27 mpg on the highway, and gas averages $3.39 along the route.
- Gallons needed: 1,280 ÷ 27 = 47.4 gallons.
- Fuel cost: 47.4 × $3.39 = $160.71.
- Per person: $160.71 ÷ 4 = $40.18 each.
Getting your numbers right
- Distance: use the route distance from your map app, and remember to double it for a round trip.
- Miles per gallon: use your car's highway rating from the window sticker or fueleconomy.gov, or better, your own measurement: fill the tank, reset the trip meter, drive, then divide miles driven by gallons needed to refill.
- Gas price: prices vary a lot between states. California is usually the most expensive, and states along the Gulf Coast are often among the cheapest. Budget with the average along your route, not your hometown price.
Real-world mileage is usually lower than the sticker when you drive fast, carry a full load, use a roof box or tow a trailer. Add 10–15% to the estimate if any of those apply.
Cost per mile
Divide the price per gallon by your mpg. At $3.50 and 25 mpg, fuel costs $0.14 a mile. It's a handy number for comparing driving with flying or taking the train.
Fuel isn't the whole cost of driving, though. Tires, maintenance and depreciation add up too. The IRS business mileage rate, around 70 cents a mile in recent years, is a good benchmark for the full cost of using a car.
Electric car?
Use the same idea with electricity: miles ÷ miles per kWh × price per kWh. A 500-mile trip in an EV that averages 3.5 miles per kWh uses about 143 kWh. At a home rate of $0.17 per kWh that's about $24; at a fast charger charging $0.45 per kWh it's about $64.
Ways to cut the cost
- Keep your tires properly inflated.
- Drive at a steady speed and use cruise control on highways; fuel economy drops noticeably at higher speeds.
- Remove roof racks and boxes when you're not using them.
- Use a gas price app to plan fill-ups in cheaper areas, and avoid buying gas right next to highway exits and airports.
- Pack light: extra weight costs fuel.
Plan your trip in seconds
The Gas Cost Calculator works out gallons, total cost, cost per mile and each person's share, with one tick for a round trip. It also supports UK mpg, L/100 km and km/L if you're driving abroad.
Frequently asked questions
How much does it cost to drive 1,000 miles?
How do I calculate gas cost per mile?
How should friends split gas money?
Tools mentioned in this guide
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