How to compare fairly
- Select the unit preset used by both economy figures.
- Enter one shared trip distance and choose one-way or round trip.
- Enter each vehicle's economy and one shared expected fuel price.
- Compare fuel required, fuel cost, and the absolute cost difference.
Formula
Vehicle fuel cost = distance ÷ vehicle MPG × shared price per gallon.
For L/100 km, litres = kilometres × L/100 km ÷ 100. Comparing the same trip and price isolates the effect of economy.
Worked comparisons
For 200 miles at $3.50 per US gallon, a 25 MPG vehicle uses 8 gallons and costs $28. A 40 MPG vehicle uses 5 gallons and costs $17.50. The fuel difference is $10.50.
| Economy | Gallons | Fuel cost | Cost per mile |
|---|---|---|---|
| 20 MPG | 25 | $87.50 | $0.175 |
| 25 MPG | 20 | $70.00 | $0.140 |
| 30 MPG | 16.67 | $58.33 | $0.117 |
| 35 MPG | 14.29 | $50.00 | $0.100 |
At 1,000 miles, the same 25 MPG and 35 MPG vehicles cost $140 and $100 respectively, a $40 fuel difference. The difference scales with distance while the assumptions remain fixed.
What the comparison means
A lower displayed fuel cost means less fuel spending for the entered trip and price. It does not establish that a vehicle is cheaper overall or better suited to the journey.
Real-world considerations
- Use economy figures measured or rated under comparable conditions.
- Passenger and cargo load, towing, terrain, traffic, weather, tires, speed, and vehicle condition can affect each vehicle differently.
- Purchase price, depreciation, insurance, maintenance, reliability, charging, taxes, and resale value are outside this fuel-only comparison.
Common questions
Is the higher-MPG vehicle always cheaper overall?
No. It has a lower fuel estimate under the shared inputs, but total ownership cost requires many other values.
Can I compare US MPG with L/100 km?
Switch both vehicles to the same preset. The calculator converts compatible entered values when the preset changes.