How is trip fuel cost calculated?

Divide distance by your fuel economy (after converting units) to get fuel needed, then multiply by the fuel price. If you use MPG, enter price per gallon; if you use L/100 km or km/L, enter price per liter.

Should I enter price per gallon or per liter?

Match the price unit to your economy unit: MPG uses price per gallon; liters per 100 km and kilometers per liter use price per liter.

Does round trip double the cost?

Yes. Round-trip cost is the one-way trip cost multiplied by two, assuming the same distance and fuel economy in both directions.

Why is actual fuel use different from the estimate?

Real-world use depends on speed, traffic, weather, cargo weight, tire pressure, and driving style. Treat the result as a planning estimate, not an exact fill-up amount.

Fuel Cost Calculator — Free Online

About this calculator

A fuel cost calculator multiplies trip distance by fuel price and divides by fuel economy to estimate trip fuel spend.

Who should use it: Drivers budgeting road trips or commuting costs.

When to use it: Use it when comparing routes, vehicles, or fuel price scenarios.

Fuel needed and trip cost

Fuel needed = Distance ÷ Economy (converted); Trip cost = Fuel needed × Fuel price; Round-trip cost = Trip cost × 2

Distance and economy are converted to a consistent pair of units (miles and gallons, or kilometers and liters). The fuel price must use the same volume unit as the economy rating — gallons for MPG, liters for L/100 km or km/L.

Step-by-step

Enter trip distance
One-way distance in miles or kilometers.
Enter fuel economy
Your vehicle’s MPG, L/100 km, or km/L rating.
Enter fuel price
Price per gallon when using MPG; price per liter for metric economy units.
Choose currency and round trip
Pick a display currency and whether to show round-trip totals.

Worked example: 100 miles at 25 MPG and $3.50/gal

A one-way 100-mile drive in a car that averages 25 MPG, with gas at $3.50 per gallon.

Fuel needed = 100 ÷ 25 = 4 gallons
Trip cost = 4 × $3.50 = $14.00
Round-trip cost = $14.00 × 2 = $28.00
Cost per mile = $14.00 ÷ 100 = $0.14

The one-way trip costs about $14; a round trip is about $28.

How to interpret the result

Real MPG varies with speed, load, and weather — treat results as estimates.

Key definitions

Fuel economy: How far the vehicle travels per unit of fuel — MPG, L/100 km, or km/L.
Trip cost: Estimated one-way fuel cost for the entered distance.
Round-trip cost: One-way trip cost multiplied by two.
Cost per mile / kilometer: Trip cost divided by distance in miles or kilometers.

Common use cases

Budgeting gas for a road trip or commute
Comparing the cost of driving vs. other transport
Estimating round-trip fuel spend before booking a rental
Converting between US and metric fuel-cost conventions

Tips

Use your real-world average MPG or L/100 km, not the brochure rating, for better estimates.
Match price units to economy units — gallons with MPG, liters with metric ratings.
Add a small buffer for traffic, hills, or carrying extra weight.

Common mistakes

Entering a liter price while using MPG

Fix: When economy is in MPG, enter the price per gallon; switch to a metric economy unit if your price is per liter.

Using one-way distance but expecting a round-trip total without enabling round trip

Fix: Set Round trip to Yes, or double the distance yourself for an out-and-back estimate.

Mixing distance units with economy units incorrectly

Fix: The calculator converts units for you — just pick the correct distance unit and economy unit for the numbers you enter.

Limitations

Does not include tolls, parking, or maintenance.
EV energy costs need a different model.