What is the formula used to calculate cost per mile based on fuel usage only.?

Miles driven divided by MPG = gallons used. Gallons used multiplied by price per gallon = total price spent for miles driven. Total cost divided into total miles = cost per mile.

Take the price of gas and divided it by your cars mpg.

Price of Gas Per Gallon/Miles Per Gallon = cost per mile.

$3.12 per gallon/ 22 mpg = 14 cents per mile.