How to determine the mpg for a car?

[Master18]

I want to know my mpg for my car, as I need it to calculate my journey costs.

I have a Nissan Almera 1.4cc year 1997.

How do I determine/or find out my car's mpg?

[Dave B.]

Originally Posted by Master18

How do I determine/or find out my car's mpg?

I'm hoping that this isn't a trick question and/or that you're not messing with us.

It's simple math - the type of car or truck you drive doesn't matter - it's the same formula for all vehicles:
Fill the tank on your vehicle COMPLETELY - as much as it will hold. (Don't overfill - I fill mine until it 'clicks off', then squeeze the pump trigger gently again until it 'clicks' a second time.)
Immediately write down the odometer reading.
Drive the car until you again need fuel.
Fill the car's tank - again completely. To be REALLY accurate, go to the same filling station and have the car pointed in the same direction as the first fill. (The reason is that most fuel tanks don't have 'regular' shapes and the position of the car - even slightly uphill or downhill - affects the amount of fuel you can put into the tank.)
Subtract the first odometer reading from the second.
Divide that number by the number of units of fuel you put in the second time.
The resulting number is your mpg.
Example: 228 miles driven divided by a fill-up of 8.34 gallons would equal about 27.34 miles per gallon.

Hehe... I keep editing this thing...
You can also do this over a longer period to get a more accurate number. You don't, however, need to fill the car every time. You just have to keep accurate records of how much fuel you purchase and calculate your mileage only at fill-ups.
Let's do another example:
1st fill-up: 27,520 miles (you don't have to write down how much fuel you purchase for this fill-up - it's not relevant to the test.)
In a few days, you make fuel purchase #1: 10.21 gallons
And then later you make fuel purchase #2: 8.73 gallons
You finally decide to end the test and make the 2nd fill-up: 7.55 gallons - odometer reading 28,275
Total fuel used: 10.21 + 8.73 + 7.55 = 26.49 gallons
Miles driven: 28,275 - 27,520 = 755 miles
755 miles driven divided by 26.49 gallons = 28.50 mpg

[Master18]

Thanks. I was hoping for a cheaper way, but guess I have no choice.

[Dave B.]

Yeah, that's the old-fashioned way.

Most newer cars (with more electronics) let you see the fuel mileage either instantaneously or over a period. I'm an old guy, so I still track my fuel mileage in a little book that I carry in the car. I also have an Excel spreadsheet that lets me just key in the data and get the answers!

[GregA]

Originally Posted by Master18

I was hoping for a cheaper way, but guess I have no choice.

I think we "old guys" have about the cheapest way possible - paper, pencil, and a few calculations. That spreadsheet Dave mentioned is good to have too.

If you track your fill-ups and odometer reading over a LONG period of time, you may even be able to see "trends" - such as when your mileage CHANGES. These can be good indicators when the vehicle needs some kind of attention - OR if and when the gas "formula" changes (we have winter & summer blends in my area).

Take Care All, Greg (another "old guy")