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Gas cost per mile is easy to calculate and can tell motorists the immediate out-of-pocket costs of their everyday trips regardless of what they drive.

By the middle of the last year, gasoline was costing Americans about 20 cents per mile (GCPM). That average might vary considerably in the next few years, but whatever it is, greater awareness of the GCPM might begin affecting not only how Americans drive, but also what, when and where they drive.

For decades, Americans have paid most attention to two motoring numbers:

  • Gasoline cost per gallon (CPG)
  • The number of miles per gallon (MPG) their vehicle normally travels. Most new cars provide the MPG and it can be determined on older cars by counting the number of miles traveled between fillups.

However, neither the price per gallon nor the MPG directly reflect everyday out-of-pocket trip costs. And neither mesurement seemed to generate much change in American driving habits until they were hit by the shocking increase in gasoline cost. Even with $4 per gallon gasoline, it was not yet clear whether those measurements would bring permanent changes in their less-than-conservative driving habits. A $45 fillup is likely viewed as a weekly necessity covering a multitude of trips, rather than a usable measure of trip-by-trip costs

IRS, AAA Provide Total Cost Per Mile

Both the Internal Revenue Service (IRS) website and the American Automobile Association (AAA) have provided figures on the total cost of driving a mile (TCPM), but those numbers includes such things as auto maintenance, insurance and depreciation. Since miles traveled have little impact on insurance costs or vehicle depreciation, the TCPM numbers do not get much attention from motorists.

The gasoline cost per mile (GCPM), however, is a hard, immediate out-of-pocket measurement that motorists can directly apply to their everyday driving routines. It can be easily translated to such specifics as the cost of pleasure trips, the wisdom of driving extra miles to shop, and whether they should use public transportation or carpooling to get to and from work. It can even help them determine whether they should drive extra miles to purchase cheaper gasoline.

The AAA website can help motorists make general estimates on both total costs per mile and gasoline costs per mile based on the size (small, medium or large) sedan they drive. Other types of vehicles are not covered. Neither are performance, age and condition differences in various makes and models.

Motorists Can Calculate Own Cost Per Mile

However, motorists can easily calculate the gasoline cost per mile for themselves and come up with a more precise answer for their individual vehicles. The calculation involves two steps:

  1. Divide one (for one mile) by the vehicle’s miles per gallon.
  2. Multiply that percentage by the cost of a gallon of gasoline.

Examples:

  • 1 divided by 20 mph = .05 (5%)
  • .05 x $4.00 (Cost per gallon) = 20 cents per mile

Changing the cost per gallon gives these gas prices per mile:

  • 5% x $5.00 = 25 cents per mile
  • 5% x $6.oo = 30 cents per mile
  • 5% x $7.00 = 35 cents per mile

Keeping the price per gallon at $4, but improving the miles per gallon gives these CPMs:

  • 1 divided by 25 mph = .04 x $4 = 16 cents per mile
  • 1 divided by 30 mph = .33 x $4 = 13.3 cents per mile

Changing both the miles per gallon and price per gallon gives these CPMs:

  • 1 divided by 25 mph = .04 x $5 pg = 20 cents per mile
  • 1 divided by 30 mph = .33 x $7 pg = 23 cents per mile