FuelTripCost guide
How to Compare Fuel Costs Between Two Cars
By FuelTripCost · Published 27 September 2026 · Updated 30 September 2026
Quick answer
Estimate fuel used for each car separately using the same trip distance. Multiply each fuel amount by the same price, then subtract the two costs.
Cost difference = |distance ÷ MPG A × price − distance ÷ MPG B × price|.
What you need
- One shared trip distance and price.
- A comparable economy figure for each vehicle.
Step-by-step method
- Use the same distance, trip type, price, and unit system.
- Calculate fuel and cost for each vehicle.
- Subtract costs to find the trip difference.
- Keep non-fuel ownership costs outside the comparison.
Worked examples
Core example
For 200 miles at $3.50 per gallon, a 25 MPG car uses 8 gallons and costs $28. A 40 MPG car uses 5 gallons and costs $17.50. The fuel difference is $10.50.
200 miles
At $3.50, 25 MPG uses 8 gallons and $28; 40 MPG uses 5 gallons and $17.50. Difference: $10.50.
500 miles
At $3.50, 20 MPG costs $87.50, 25 MPG $70, 30 MPG $58.33, and 35 MPG $50.
1,000 miles
At $3.50, 25 MPG costs $140 while 35 MPG costs $100, a $40 fuel difference.
Keeping the comparison fair
Use one distance, trip type, price, and unit system for both vehicles. Economy figures should come from comparable conditions; pairing one measured city value with another vehicle's highway rating does not isolate vehicle efficiency.
If the vehicles use different fuel types or prices, run separate calculations and explain that both economy and price contribute to the difference.
What fuel savings do and do not show
The trip difference grows in direct proportion to distance while each economy and price assumption stays fixed. Testing 100, 500, and 1,000 miles shows how repeated use changes the fuel-only total.
Fuel savings alone cannot establish which vehicle is cheaper to own. Purchase price, financing, depreciation, insurance, maintenance, repairs, taxes, charging, and suitability require separate evidence.
Real-world considerations
- Compare the same distance and fuel-price assumptions.
- Fuel cost alone does not determine overall ownership cost.
- Use actual MPG figures from similar conditions when available.
Common mistakes
- Using different prices or distances for the two cars.
- Comparing US MPG with Imperial MPG directly.
- Claiming fuel savings prove lower total ownership cost.
How to make the estimate more useful
- Use economy values from similar conditions.
- Compare multiple distances to understand how the fuel difference scales.
Limits of this calculation
The comparison covers entered fuel expense only and cannot judge purchase price, reliability, insurance, charging, maintenance, or suitability.
Questions
Is the higher-MPG car always cheaper overall?
Not necessarily. This comparison only covers fuel for the entered trip, not purchase price, repairs, or insurance.
Does the fuel-cost difference scale with distance?
Yes, while fuel price and each vehicle's economy remain fixed. Doubling distance doubles each fuel estimate and the difference between them.
Why use the same fuel price?
A shared price isolates the effect of fuel economy.
Use the calculation
Try the vehicle comparison calculator or review the calculation methodology and unit constants.