Answer: Enter your values and the Fuel Cost Calculator returns the exact result instantly — formula, worked example, and a plain-English explanation are included below the tool.
Calculate trip fuel costs and plan your travel budget.
Calculate trip fuel costs based on distance, fuel efficiency, and gas prices. Works with both US (mpg) and metric (L/100km) units. The math is simple — fuel needed is distance divided by efficiency, and cost is fuel multiplied by price — but the inputs deserve care, because real-world fuel economy varies with speed, load, terrain, and temperature.
The table below shows the fuel needed and cost for a 300-mile trip at $3.50 per gallon across the efficiency range of typical vehicles. A new car in the U.S. averages roughly 25-30 mpg combined per EPA data; hybrids run well above 45, and large trucks or SUVs can sit below 20.
| Vehicle efficiency | Gallons for 300 mi | Fuel cost @ $3.50/gal | Cost per mile |
|---|---|---|---|
| 15 mpg (large truck/SUV) | 20.0 gal | $70.00 | $0.233 |
| 20 mpg | 15.0 gal | $52.50 | $0.175 |
| 25 mpg | 12.0 gal | $42.00 | $0.140 |
| 30 mpg (typical sedan) | 10.0 gal | $35.00 | $0.117 |
| 40 mpg | 7.5 gal | $26.25 | $0.088 |
| 50 mpg (hybrid) | 6.0 gal | $21.00 | $0.070 |
Reading the table: halving efficiency roughly doubles cost per mile, which is why efficiency dominates lifetime fuel spend far more than small price swings at the pump. Over 12,000 miles a year, the gap between a 20-mpg and a 40-mpg vehicle at $3.50/gal is $1,050 annually.
Two unit systems meet in this calculator. U.S. drivers think in miles per gallon; most of the world reports liters per 100 kilometers. The conversion is not a simple reciprocal across distance units — 1 mile is 1.60934 km and 1 U.S. gallon is 3.78541 liters — so 30 mpg equals about 7.8 L/100km, and 8 L/100km equals about 29.4 mpg. Imperial gallons (used in the UK for fuel economy references) are larger, 4.546 liters, so UK "mpg" figures cannot be compared to US mpg directly. If you enter distance in kilometers with efficiency in mpg, the calculator converts the distance to miles first, then applies your mpg figure, keeping the arithmetic consistent either way.
The EPA fuel-economy figures on a new-car window sticker come from laboratory tests adjusted downward to approximate real driving; your actual mileage usually lands within a modest band of the sticker but can drift below it in certain conditions. The biggest factors: highway speeds above about 50-60 mph increase aerodynamic drag steeply, so sustained 80-mph cruising can cost several mpg versus the sticker highway number; cold weather and short trips reduce economy because engines run rich and never fully warm; roof cargo boxes can cut highway economy noticeably; and underinflated tires add rolling resistance. Towing or a heavily loaded vehicle can drop fuel economy 15-30% on the highway. The U.S. Department of Energy's fueleconomy.gov, which publishes official figures, also notes that aggressive driving (rapid acceleration and hard braking) can lower gas mileage by roughly 15-30% at highway speeds and around 10-40% in stop-and-go traffic.
Electric vehicles change the arithmetic rather than end it. An EV consumes energy in kilowatt-hours, so the parallel calculation is distance multiplied by consumption (commonly around 0.25-0.35 kWh per mile for mainstream EVs, per EPA-rated figures) times your electricity price per kWh. Home charging at the average U.S. residential rate of roughly 15-17 cents per kWh usually beats gasoline per mile by a wide margin, while public DC fast charging, priced per kWh or per minute and often well above residential rates, can narrow or erase the gap. Road-trip planning in an EV also means building charging stops into the route, since a 300-mile drive may require a 30-45 minute fast-charge stop, and cold weather can cut effective range materially.
For trip planning, a practical habit is to budget with a margin: take your expected efficiency, subtract 10-15% for a loaded car, mountains, or AC-heavy summer driving, and use a fuel price at the high end of the range along your route. Prices routinely vary 30-50 cents per gallon between states due to taxes, and more between stations near highways versus in town.
How do I calculate fuel cost for a trip? Divide the trip distance by your vehicle's fuel efficiency to get gallons needed, then multiply by the fuel price. For a 300-mile trip at 30 mpg and $3.50/gal: 10 gallons × $3.50 = $35.
How do I convert L/100km to mpg? Divide 235.215 by the L/100km figure: 8 L/100km ≈ 29.4 mpg (U.S.). The constant embeds both the liter-to-gallon and kilometer-to-mile conversions.
Why is my real mileage lower than the sticker? Sticker figures are lab-derived estimates; speed, cold starts, load, tire pressure, and aggressive driving all push real-world economy below the EPA numbers.
Does city or highway driving cost more in fuel? Per mile, city driving usually costs more — stop-and-go traffic burns more fuel than steady cruising for most gasoline vehicles, which is why hybrids, which recover braking energy, invert this pattern.
How much cheaper is a 40-mpg car than a 25-mpg car? At $3.50/gal, roughly 5.3 cents per mile — about $630 a year at 12,000 miles. The gap widens with fuel prices and annual mileage.