Gas Cost Calculator
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About Trip Fuel Costs
“How much will gas cost?” is the first real question of every road trip, and the mental math (distance ÷ economy × price, in three different units) is annoying enough that most people just guess. Guessing badly matters when four friends are splitting it or you're comparing driving against a flight.
Enter distance, your car's realistic economy, and the local pump price — in US or metric units. Toggle round trip, add the passenger count, and you get total fuel, total cost, and the per-person share. For multi-leg trips, run each leg or just sum the distances.
Driving abroad? Convert the pump price first with the Currency Converter
The Fuel-Cost Formula
Same math, two unit systems:
US: gallons = miles ÷ MPG cost = gallons × $/gal Metric: liters = km × L/100km ÷ 100 cost = liters × $/L
Worked example: 300 miles at 30 MPG needs 10 gallons — $35.00 at $3.50/gallon, or $70.00 round trip, $17.50 each with four people splitting. Metric: 500 km at 8 L/100km is 40 liters — $64.00 at $1.60/L.
Cost per 100 Miles by MPG
At $3.50/gallon — why economy differences compound over a road trip:
| Fuel economy | Gallons /100 mi | Cost /100 mi | Cost for 1,000 mi |
|---|---|---|---|
| 20 MPG (truck/SUV) | 5.00 | $17.50 | $175 |
| 25 MPG (crossover) | 4.00 | $14.00 | $140 |
| 30 MPG (sedan) | 3.33 | $11.67 | $117 |
| 35 MPG (compact) | 2.86 | $10.00 | $100 |
| 40 MPG (hybrid) | 2.50 | $8.75 | $88 |
| 50 MPG (efficient hybrid) | 2.00 | $7.00 | $70 |
The gap between the truck and the hybrid is about $105 per thousand miles at these prices — cross-country, that's real vacation money.
Squeezing the Number Down
The levers that actually move a trip's fuel bill:
- Speed: aerodynamic drag grows with speed squared — most cars burn noticeably more per mile at 80 mph than at 65.
- Roof cargo: boxes and racks can cut highway economy dramatically; put weight inside or on a rear hitch when possible.
- Tires: underinflation costs economy and safety — check pressures cold before a long trip.
- Fuel stops: apps and station clusters off cheaper exits beat highway-plaza pricing by enough to matter on a long haul.
- Real MPG: track a few tanks (miles ÷ gallons at fill-up) — that number beats the sticker and makes this calculator honest.
None of these change the formula — they change the economy figure you feed it.
Frequently Asked Questions
How much does gas cost for a 300-mile trip?
Distance ÷ MPG × price: at 30 MPG and $3.50/gallon, 300 miles costs $35 one way, $70 round trip. A 20-MPG vehicle pays $52.50 for the same one-way run — enter your own numbers above.
How do I figure out my car's real MPG?
Fill the tank, reset the trip odometer, drive normally, and at the next fill-up divide miles by gallons pumped. Repeat over 2–3 tanks and average. Real-world figures commonly run below the sticker's combined rating — that's the number worth using here.
How do I convert L/100km to MPG?
Divide 235.2 by the L/100km figure: 8 L/100km ≈ 29.4 MPG (US). Note that in L/100km, LOWER is better — and this calculator's metric mode takes it directly, no conversion needed.
Is driving cheaper than flying?
For fuel alone, driving often wins for 2+ people over moderate distances — but the honest comparison adds tolls, meals, lodging on long routes, and wear at roughly the IRS-style per-mile figure. Solo long-haul trips flip toward flying quickly.
How should we split gas on a road trip?
The simplest fair split is total fuel cost ÷ everyone including the driver — the calculator does it with the people field. A more generous convention adds a bit extra to compensate the owner for wear; agree before departure, not at the pump.
Does this include tolls and wear and tear?
No — it's fuel only. Tolls are route-specific (check your mapping app), and total operating cost including depreciation and maintenance runs several times the fuel figure per mile, which matters if you're reimbursing a driver rather than splitting a pump receipt.
Methodology. This calculator uses standard financial formulas used across the industry. It is reviewed and maintained by the Vast Calculators editorial team.
Last updated · July 2026
Disclaimer. This tool provides estimates for general informational purposes only and is not a substitute for professional financial advice. Always consult a qualified financial advisor before making decisions about your finances.