Fuel budgeting starts with distance and efficiency
Fuel cost is a direct consequence of three variables: how far you drive, how efficient the vehicle is, and how much each gallon costs. Because fuel economy is expressed as miles per gallon (MPG), the gallons required for a journey are found by dividing distance by efficiency.
This makes fuel planning a ratio problem rather than a flat lookup. A vehicle that gets 30 MPG uses half the fuel of a vehicle that gets 15 MPG over the same route. That difference becomes meaningful in annual commuting budgets, road-trip planning, and delivery or rideshare economics.