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).

## 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:

- Miles at the start of the tank (first fill)
- Miles at the end of the tank (second fill)
- Gallons used

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

(end – start) = miles driven

Miles Driven / Gallons Used = MPG

So:

**The Miles per Gallon Formula is:**

**The Miles per Gallon Formula is:**

**Miles per Gallon Calculator**

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

*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.*

**average cost of gas per year****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
- Inflation Adjusted Gasoline Prices
- Gasoline vs. Crude Oil Prices
- Historical Gas Price Chart
- Current Average Cost of Gas by County
- Gasoline Taxes by State
- Average Cost of Gas Per Month
- Regarding Gas Inflation
- Gasoline Rewards Credit Cards
- More Inflation Adjusted Prices

Image courtesy of Salvatore Vuono/FreeDigitalPhotos.net

### About Tim McMahon

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Brad says

Tim,

If my annual gas cost was $860.31 and my tank holds 25 gallons and I paid an average of $2.00 per gallon and I average 15 miles to the gallon then how many miles were driven in 1 year?

Thanks,

BK

Tim McMahon says

Brad, Tank size is irrelevant.

Total Cost / (cost/gal)= gallons

Gal x (Miles/Gal) = Miles

So in your case that would be:

$860.31 /$2 = 430.155 gal

430.155 x 15 = 6,452.325 miles

The key is to sort your units so they cancel out and remember if you divide you invert and multiply.

Nancy Averitt-Campbell says

how much will it cost me to drive 90-getting 10 miles to gal.at $4.00 a gallon?

Tim McMahon says

To figure this out is a two step process. First how many gallons would you use?

To drive 90 miles getting 10 miles per gallon you would use 9 gallons.

90 miles / 10 mpg= 9 gallons

Why Divide by mpg?

Always remember mpg means miles per gallon and “per” always means “divided by”.

It always helps to sort out the units so you can find out the formula.

MPG could be written as m/g. So the units would be as follows: miles / (miles/gallon) = gallons.

Why? Invert and multiply. So miles / (miles/gallon) also equals miles x (gallons / miles)

Since you have one “miles” on top and one on bottom the miles cancel and you are left with gallons.

To find the answer (Dollars) use the formula: gallons x (Dollars per gallon) = Dollars

So 9 gallons at $4/gal = 9 x 4.00 = $36.00

Hope this helps!