Calculating Miles Per Gallon

As the cost of gas goes up it becomes more and more important to use it more efficiently and therefore people become more interested in how much it is costing to drive a mile. It is relatively easy to calculate how many miles per gallon you are getting. Some cars actually calculate it for you as you are driving. But if yours doesn’t calculate the miles per gallon, you can easily do it yourself (although not “on the fly” as you are driving).

Calculating Miles Per Gallon

How to Calculate Miles Per Gallon

Simply fill up your gas tank (make sure it is full i.e. the pump shuts off) and write down the mileage from your odometer. Then the next time you fill up (make sure it is as full as it was the first time) and write down the number of gallons (from the gas pump) and the mileage again from your odometer.

Calculating Miles Per Gallon (mpg)

Now you have three numbers on your piece of paper, they are:

  1. Miles at the start of the tank (first fill)
  2. Miles at the end of the tank (second fill)
  3. Gallons used
The formula for calculating Miles Per Gallon is simply miles driven divided by gallons used. So to calculate the miles driven you take the miles at the end of the tank and subtract the Miles at the start of the tank, and then you divide that by the total gallons of gas used.

Here is the formula for calculating Miles per Gallon (MPG):

(end – start) = miles driven

Miles Driven / Gallons Used = MPG


The Miles per Gallon Formula is:

S= Miles at the start of the tank (when filled first)
E= Miles at the end of the tank (when refilled)
G= Gallons used
Or you can just use our Miles per Gallon Calculator

Miles Per Gallon


Enter Data Below
Enter only numeric values (no commas), using decimal points where needed. Non-numeric values will cause errors.
Mileage at Start
Mileage at End
Gallons Used

Average Miles Per Gallon
If Result is negative you have reversed the end and the start mileage.


If you’d like to see the average cost of gas in the U.S. or how gasoline prices have compared to overall inflation see  Inflation adjusted Gasoline Prices.

Once you know your average miles per gallon (mpg), you can use our Cost of Gas per Month calculator to estimate how much you are spending on gasoline in an average month from this it will estimate your average cost of gas per year as well.  By knowing how much you spend on gas you can get a better handle on your monthly commuting expenses and your overall budget.

See Also:

Cost of Gas

Calculating the Cost of Gas per Month

Gas Prices (nominal and inflation adjusted)

Crude Oil Prices (table)

Oil Price History (Chart)

Cost of Living comparison between any two cities in the U.S.

 Rate of Inflation


Image courtesy of Salvatore Vuono/


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