There are a couple of ways. One is to reset your trip meter every time you fill up and use the miles from the last trip divided by the gallons used to fill the tank. No need to wait until empty as long as you reset the trip meter each time. Another is to note the miles on the odometer on every tank. Subtract the old reading from the new to get your miles traveled and then divide by the gallons used to fill the tank. There are apps you can use to keep track of your MPG over time. See my signature below.

 

There are a couple of ways. One is to reset your trip meter every time you fill up and use the miles from the last trip divided by the gallons used to fill the tank. No need to wait until empty as long as you reset the trip meter each time. Another is to note the miles on the odometer on every tank.
Subtract the old reading from the new to get your miles traveled and then divide by the gallons used to fill the tank. There are apps you can use to keep track of your MPG over time. See my signature below.

Being an economist and therefore anal-retentive-for-life, I use both of the (non-app) ways noted by Hacksaw. (FYI, I've found an additional benefit to this method: the more intense calculations give great exercise to my fingers and toes!)

 

If you have iPhone, Roadtrip is a good app the use.

I forget the name of the app I used with my old Galaxy S5...

 

Divide your miles traveled by the gallons filled.
If you've gone 300 miles and you put 10 gallons into your car, you got 30 mpg.
This only works if you fully fill up the car because that's the only way to know how much gas you used compared to the last time you filled up. To start you need to fill up the car. Then the next time you fill up you can calculate.
I recommend using fuelly to track your fuel consumption. It takes the calculation out of it and tracks your fuel consumption over time.


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Great thanks everyone! Now I know how to do it. I'll update when I go this afternoon to fill her up.

BTW. My name is Barbara and my nickname is Babu. I'm trying to come up with a cute vanity plate name for my car. I say Babu because it rhymes with Subaru. Any cute suggestions?

 

Welcome to the Forvm! :icon_welcome:

How many letters are you allowed to use? How about "BabuSubu" ?

 

Good question! I live in NYC. I think we are allowed up to 8 letters/numbers so that would be perfect! That is a real good one. I don't know why I didn't think of that!

 

Or Subabu


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I love this one too!! I can add numbers to the end of it like my bday or something! Subabu112!! Oh wait....that would be 9 letters or numbers then! Darn!

 

Told my sister yesterday about this. You fill up your gas tank, zero out the trip odometer. Drive as far as you can go, like last bar on fuel gauge. The more miles the better the accuracy you're going to get. Fill up gas tank, wright down how many gallons it took. Take the miles off your trip odometer, divide gallons into the miles. If you used 10 gallons and went a 100 miles, it would be 10 mpg. 50 Hilarious Car License Plates - Mentertained

 

There is something to be said for monitoring not just one's MPG, but the MPG based on the Grade of gas. 87, 89, 91, 93 octane, and whether there is ethanol in it impact MPG. Some gas has ethanol in it. There is ENORMOUS negative impact on engines from ethanol. Despite the 2.0 Boxer engine being capable of running on 87, in states like CT many know first hand as a vehicle ages the 10% ethanol takes a horrific toll on the engine and emission related items. Some have found they can get by on 89, but if you live on a state border and can avoid gas with ethanol, you will Never regret not using it. Likewise higher octane can afford higher MPG. How hard a car is working and personal driving habits play a big role too. There's a big difference between climbing hills and mountains, and easy flat highway driving.

An easy approach is start with the best gas, write down the mileage on the odometer after filling up and you have a full tank. Keep a log of you receipts, how much gas you put in as you go, and each time after you fill up, record the mileage again. You can calculate your MPG between full tanks or multiple full tank readings. I've found higher octane gas provides better gas mileage, however, the price between grades if you are looking for the most economical break may have you realizing what you actually pay for the gas also plays a big role. In other words, you get more MPG with higher octane gas, but chasing 93 may or may not be the most cost effective MPG. Again, how and where you drive is a big influence, and more important than the gas you put in, CHECK THE OIL FREQUENTLY. If you are burning an unexpectedly large amount of oil, keep in mind there have been two technical service bulletins (TSB) one that Subaru replaces the rings, another in which the block gets replaced (TSB 2002-157-14R), though these focus on models before the 2015 XV. Once you are over 60k if you miss a problem it will be on you - $$$. The 2.0 remains a better historically performing engine than the 2.5, and now with Synthetic in it right out of the factory oil changes every 6k and at times more often depending on the driving conditions are SUPER important!

 

Where are you finding ethanol free gas? Last time I checked it was federally mandated at all "car" gas stations. The only places it's available is in marinas or air ports.


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Where are you finding ethanol free gas? Last time I checked it was federally mandated at all "car" gas stations. The only places it's available is in marinas or air ports.


Ethanol-free gas stations in the U.S. and Canada

 

With ethanol-free gas running more than $2/gallon more than "regular" gas where I live, no thank you.