How do I calculate gas cost for a trip?

Divide trip distance by your car's MPG to get gallons, then multiply by price per gallon. 300 miles ÷ 28 MPG = 10.7 gallons × $3.50 = $37.50. The calculator does this plus all the unit conversions (km, liters, L/100km) automatically.

What's a fair way to split gas with passengers?

Two defensible methods: split the fuel cost evenly among everyone including the driver, or have passengers cover the full fuel cost while the driver contributes the car. For regular carpools, the second is common because the driver also eats depreciation and maintenance — fuel is only about half the true per-mile cost of driving.

How does L/100km convert to MPG?

They're inverse measures: MPG (US) = 235.21 ÷ L/100km. So 8 L/100km ≈ 29.4 MPG, and 6 L/100km ≈ 39.2 MPG. Because of the inversion, a 1-unit improvement in L/100km matters much more at the thirsty end (12→11) than the efficient end (5→4).

Is driving cheaper than flying?

On fuel alone, driving usually wins for 1 person on routes under ~500 miles, and almost always wins with 3-4 people sharing. But add the honest extras: wear at roughly another 12-15¢/mile, tolls, parking, and a hotel night if the drive exceeds a day. For solo trips over 700 miles, a sale-fare flight frequently beats the all-in cost of driving.

Should I use premium gas to get better mileage?

Only if your engine requires it. In a car designed for regular, premium doesn't measurably improve economy or power — modern engines tuned for 87 octane gain nothing from 93. If the manual says 'premium recommended' (not required), the typical gain is small enough that regular is usually the cheaper per-mile choice.

Money & Finance · Free tool

Fuel Cost Calculator

Estimate fuel cost for any trip — distance, MPG, price per gallon. Great for pricing a drive vs flight.

Updated June 2026

DistanceDistance unitFuel economyEconomy unitFuel pricePrice unit

Fuel needed

40.56 L (10.71 gal US)

Cost per mi

$0.13

Total trip cost

$37.50

Distance: 482.8 km equivalent

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What it does

Estimate fuel cost for a drive: distance, MPG (or L/100km), and price per gallon or liter. Useful for budgeting a road trip, comparing driving vs flying, and splitting costs fairly with carpoolers.

Pair with trip cost calculator, budget calculator, expense split calculator, and length converter.

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Paste this snippet into any page. Loads on-demand (lazy), no tracking scripts, and sized to most dashboards. Replace the height to fit your layout.

<iframe src="https://freetoolarena.com/embed/fuel-cost-calculator" width="100%" height="720" frameborder="0" loading="lazy" title="Fuel Cost Calculator" style="border:1px solid #e2e8f0;border-radius:12px;max-width:720px;"></iframe>

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Example input & output

Input

Distance: 300 miles
Fuel economy: 28 MPG (US)
Gas price: $3.50/gallon

Output

Fuel needed: 10.71 gallons
Total cost: $37.50
Cost per mile: $0.125

Highway MPG beats the window-sticker combined figure; city driving undercuts it. For a long highway trip, your real economy is usually a bit better than the rating.

How to use it

Pick units — miles/gallon or km/litres.
Enter distance, vehicle MPG, and fuel price.
Add round-trip toggle and passenger count.
Read total cost and per-person share.

How it works

Everything is normalized to liters and kilometers internally, then converted back. For MPG: gallons = distance ÷ MPG, cost = gallons × price per gallon. For metric: liters = km ÷ 100 × L/100km. The unit constants are exact: 1 mile = 1.609344 km, 1 US gallon = 3.7854 L, 1 UK gallon = 4.5461 L.

Common mistakes when using this tool

Mixing US and UK gallons. A UK gallon is 20% bigger, so 40 MPG (UK) ≈ 33 MPG (US). British fuel-economy figures look better than American ones for the same car.
Entering one-way distance for a round trip. The tool computes exactly the distance you give it — double it yourself for the return leg.
Using the optimistic dashboard MPG. Trip computers often read 5-8% high. Tank-to-tank math (miles driven ÷ gallons at fill-up) is the honest number.

When to use this tool

Any trip where you know distance, your vehicle's economy, and local fuel price.
Mixed-unit situations — it converts between MPG (US/UK), L/100km, and km/L, and between per-gallon and per-liter prices.
Recurring commutes: run your weekly mileage once to see the monthly fuel budget.

When not to use it

Total cost-of-driving questions — fuel is only part; depreciation, tires, and maintenance roughly double the per-mile cost (the IRS rate exists for a reason).
EVs — cost per mile is kWh-based; use the EV charging cost calculator.
Tax-deduction mileage claims — use the IRS standard mileage rate, not actual fuel cost.

Common use cases

Budgeting the gas line of a road trip before booking anything else.
Splitting fuel fairly with carpoolers using the per-mile figure instead of guessing.
Comparing the true cost of driving vs a $120 flight for a 600-mile trip.
Reimbursing a friend who drove: distance × cost-per-mile is defensible math.

Frequently asked questions

How do I calculate gas cost for a trip?: Divide trip distance by your car's MPG to get gallons, then multiply by price per gallon. 300 miles ÷ 28 MPG = 10.7 gallons × $3.50 = $37.50. The calculator does this plus all the unit conversions (km, liters, L/100km) automatically.
What's a fair way to split gas with passengers?: Two defensible methods: split the fuel cost evenly among everyone including the driver, or have passengers cover the full fuel cost while the driver contributes the car. For regular carpools, the second is common because the driver also eats depreciation and maintenance — fuel is only about half the true per-mile cost of driving.
How does L/100km convert to MPG?: They're inverse measures: MPG (US) = 235.21 ÷ L/100km. So 8 L/100km ≈ 29.4 MPG, and 6 L/100km ≈ 39.2 MPG. Because of the inversion, a 1-unit improvement in L/100km matters much more at the thirsty end (12→11) than the efficient end (5→4).
Is driving cheaper than flying?: On fuel alone, driving usually wins for 1 person on routes under ~500 miles, and almost always wins with 3-4 people sharing. But add the honest extras: wear at roughly another 12-15¢/mile, tolls, parking, and a hotel night if the drive exceeds a day. For solo trips over 700 miles, a sale-fare flight frequently beats the all-in cost of driving.
Should I use premium gas to get better mileage?: Only if your engine requires it. In a car designed for regular, premium doesn't measurably improve economy or power — modern engines tuned for 87 octane gain nothing from 93. If the manual says 'premium recommended' (not required), the typical gain is small enough that regular is usually the cheaper per-mile choice.

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