Estimate how much a road trip or your daily commute costs in gas.
The formula is simple: divide your trip distance by your vehicle's miles per gallon (MPG), then multiply by the price per gallon of gas.
For example, a 300-mile trip in a car that gets 28 MPG with gas at $3.25/gallon: 300 / 28 = 10.71 gallons x $3.25 = $34.82. The cost per mile is $3.25 / 28 = about $0.116.
The biggest factors affecting MPG are speed (optimal is usually 45-65 mph), tire pressure, vehicle maintenance, driving habits (smooth acceleration vs. aggressive), and weight. Air conditioning at highway speeds is more efficient than open windows due to aerodynamic drag. City driving typically yields 15-30% worse fuel economy than highway driving.