How to Calculate MPG by Miles per Gallon Pumped

How to calculate MPG correctly by miles per gallon of gas pumped without using any fancy devices? There is a very simple and easy process that I use which I’m going to teach you right now. It also happens to be the best way to calculate gas mileage because it’s accurate and directly connected to how much you are spending at the pump.

However, many motorists are still confused as to how to do it properly. The main problem is people don’t understand that to measure properly, you don’t measure how much gas you burn outright – you measure how much gas you put in to calculate how much you burned during the time you last filled the tank. In other words, the gas you put in to fill the tank can tell you exactly how much you used in your previous trip. Simple enough.

For this to work you have to fill up your tank before you start measuring and then fill it again completely when you are ready to finish the measuring process. You don’t even have to wait until the tank is empty to take a measurement – so long as you burn through at least a quarter or half a tank in order to get a proper average.

This process is the most accurate way of measuring MPG consumption without using any technical equipment…

This process is the most accurate way of measuring MPG consumption without using any technical equipment or special computers plugged into your engine. Also, because MPG meters in trip computers vary so much from car to car, they are not a reliable way of comparing MPG from car to car. For example, I’ve found the MPG meter in my Ford Mustang is usually about 2 MPG off.

The proper way of calculating miles per gallon is the way I outline below:

1. Fill the tank until the gas pump nozzle clicks once. Stop.

2. Get back in the car and before setting off, jot down the miles on the odometer. This is the most important bit, because if you forget to jot the mileage on the car after filling the tank, you have to start over. For this example we’ll say the car reads 80,000 miles.

3. Drive as you normally would for the next few days. You don’t have to go through the entire tank of fuel, but if you do, make sure to get back to a gas station as soon as the low gas light comes on. Alternatively drive until you’re at half a tank, or whatever, it doesn’t really matter – you can measure anyway because the measuring comes later.

4. Swing by a gas station and fill your tank again until the nozzle clicks and stops, ONCE. Don’t continue filling past that first click because it can skew your numbers.

5. Note how many gallons of fuel you pumped in – you can use your receipt for that. Remember, it doesn’t matter if the tank wasn’t empty to begin with. For this example, let’s say you pumped 10.5 gallons. That’s how much gas you burned since your last fill up.

6. Now, before you take off look at the current miles on the odometer. For this example let’s say the odometer reads 80,200 miles.

7. Subtract the odometer number you jotted down during your last fuel up from the current odometer reading. In this example 80,200 – 80,000 = 200 (how much you drove on the amount of fuel you just pumped back in. Simple.)

8. Now simply divide those miles driven by the gallons pumped. In this case, 10.5 gallons. So, 200 miles divided by 10.5 galons = 19.047619 – Round down to 19.

9. That’s it, 19MPG.

You might be surprised to find that this number is probably lower than what the manufacturer claims to the be the average for your vehicle. This will depend on your driving conditions, driving habits, quality of gas and condition of vehicle among other factors.

That’s it. Now you can keep a log on an Excel spreadsheet with every fuel up in order to keep track of how much you are spending or any changes in gas consumption you might have to be concerned about. A log can help you determine differences when you do a lot of freeway driving versus times you mainly stick to the city. When you calculate gas mileage like this, you can also see differences in MPG during different seasons – for example, winter vs summer.

You don’t have to do this every time you fuel up, unless you want a complete record of your vehicle’s gas mileage. However, as a responsible motorist, you should take an MPG calculation like this at least a couple of times per year. I keep a complete log with all my gas mileage calculations – by contrast, my spouse doesn’t. But she still does her MPG calculations at least a few times a year.

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