Fuel Cost Calculator

How Trip Fuel Cost Is Calculated

Estimating a trip's fuel cost is a two-step calculation: first find how many gallons the trip will actually take by dividing distance by your vehicle's MPG, then multiply that gallons figure by the price per gallon to get a total dollar cost. This makes it easy to budget a road trip in advance, or compare the fuel cost of two different routes or two different vehicles for the same trip.

$$\text{Total Cost} = \left(\frac{\text{Distance}}{\text{MPG}}\right) \times \text{Price per Gallon}$$

Worked Example

A 300-mile trip in a vehicle averaging 25 MPG needs 300 ÷ 25 = 12 gallons of fuel. At 3.50 dollars per gallon, total fuel cost = 12 × 3.50 = 42 dollars. This kind of quick estimate is useful for trip budgeting, comparing two possible routes of different lengths, or comparing how two different vehicles would each cost to drive the same trip.

Metric Version (km and Liters)

Outside the US, the same estimate works in kilometers and liters, with fuel economy expressed as liters per 100 kilometers (L/100km) instead of miles per gallon. Switch the US/Metric dropdown above to enter trip distance in kilometers, fuel economy in L/100km, and price per liter — the calculator converts your currently entered figures automatically rather than resetting them. Note that fuel economy runs the opposite direction in the two systems: a higher MPG is more efficient, but a lower L/100km is more efficient.

$$\text{Total Cost} = \left(\text{Distance} \times \frac{\text{L/100km}}{100}\right) \times \text{Price per Liter}$$

MPG and L/100km are reciprocals of each other rather than a simple unit conversion, so switching units converts the fuel-economy figure itself, not just distance and price: L/100km is approximately 235.21 divided by MPG, and MPG is approximately 235.21 divided by L/100km.

Common Mistakes

Using the wrong MPG figure for the conditions is a frequent error — city MPG applied to a highway-heavy road trip (or the reverse) can meaningfully skew the estimate, since real fuel economy depends heavily on which kind of driving actually matches the trip. It's also easy to forget that price per gallon varies significantly by region and even by state, so assuming one flat price for a long trip that crosses state lines can leave the estimate noticeably off from the actual cost at the pump.

Terms You Should Know

MPG — miles per gallon, the standard measure of how far a vehicle travels per gallon of fuel.

Combined/City/Highway MPG — separate MPG ratings for different driving conditions; combined blends city and highway, and using the rating that best matches the actual trip gives the most accurate cost estimate.

Fuel Budget — the portion of a trip's total cost set aside specifically for gasoline, separate from lodging, food, or tolls.