Calculate Your Car's MPG

Tuesday, 26 October 2010 06:00

Calculate Your Car's MPG

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Do it yourself

Sure, calculating your fuel economy sounds simple. After all, the unit of measurement itself tells you all you need to know: miles per gallon. Just take how many miles you've driven and divide it by how many gallons of fuel you've used.

To make sure that your numbers are accurate, you could carry a chart in the glovebox where you

write down exactly how many miles you've driven between visits to the gas station. Make sure you fill up all the way and record how many gallons you put in the tank, then perform some simple math.

Of course, that would take up a lot of time and wouldn't necessarily be accurate. Variations in temperature can cause your fuel tank to lose capacity of up to a gallon of gas, and your mileage might not be accurate if you've got aftermarket wheels or tires on your car.

There's an app for that

Smartphone apps such as MPG and Gas Cubby can replace your log book and long division with a neat display that include graphs of fuel economy over time and calculations of how much you've spent on gas. The apps can also convert units from miles to kilometers and gallons to imperial gallons or liters.

There are also easy to use web apps that allow for just as much tracking over time. Fuelly has all of the features of the dedicated mobile apps, works on your normal browser and also features a mobile browser.

Let your car do the math

From the digital display on the dash of the early '80s Chrysler Imperial to the vacuum gauge used by BMW, cars have given drivers real-time feedback on their fuel economy for decades. Lots of vehicles feature electronic trip computers that will calculate gallons of fuel used, the average fuel economy of your last trip, or miles left until zero.

If your car doesn't have a fuel economy gauge on the dash, you can install one. Most gauges out there are meant to plug into an OBD-II port, meaning that if your car was sold in the US, it would have to be from model year 1996 or newer.

Depending on what data the dashboard gauge uses, however, the numbers may not match up. The caveats about temperature and wheel size still apply, and some car owners often report consistently imprecise measurements when compared with their own measurements. That's why it's best to double-check with another way of measuring.