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As gas prices rise, fuel efficiency is becoming more and more of a critical factor. Knowing your car's MPG (that is, how many miles it gets per gallon) can help you determine if it's a gas guzzler that's eating up your cash. Once you figure out the MPG, you can do many useful things, like calculate how much a 10¢ rise in gas prices will affect your budget, how getting a car with better MPG will lower your monthly costs, or if your car is getting fewer MPG than it should, that you need it serviced. We'll show you how to do it.
Steps
Help Calculating Fuel Efficiency
Method 1
Method 1 of 4:Calculating Your Own Car's Fuel Efficiency

1Go to the gas station and fill up the fuel tank. This may sting a little, but it is key to getting an accurate reading.^{[1] X Research source }

2Record the mileage. Before even pulling away from the pump, write down your current mileage. We will call this Mileage A.^{[2] X Research source }Advertisement

3Drive normally. To get as accurate a reading as possible, drive until the tank is less than half full. The longer you can go before getting gas, the better.

4Fill up the tank again.^{[3] X Research source } Try to use the same station using the same pump as the first fill up, as pumps may be calibrated differently. This time, pay attention to how many gallons it takes to fill up the tank. This is usually shown at the pump. We will call this Gallons.

5Record the mileage again. This number we will call Mileage B.

6Do the math. The formula for determining your MPG is this:^{[4] X Research source }
 MPG = (Mileage B  Mileage A)÷Gallons.
 Subtract Mileage A from Mileage B. This will give you the number of miles you drove since your last fillup.
 Divide your answer by the number of gallons (Gallons B) it took to fill up your tank. This will give you your car's MPG.
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Method 2
Method 2 of 4:Example
Let's say you have a new car and want to track its mileage:
 Trip A: Added 8.663 gal at 3,117 mi
 Trip B: Added 9.251 gal at 3,579 mi
 Trip C: Added 8.876 gal at 4,017 mi
Method 3
Method 3 of 4:Mileage Calculation Answers
 Trip A: Baseline, does not count.
 Trip B: (3,579 mi  3,117 mi) / 9.251 gal = 49.9 mpg
 Trip C: (4,017 mi  3,579 mi) / 8.876 gal = 49.3 mpg
Method 4
Method 4 of 4:Additional Accuracy

1Verify your odometer. Not all cars reflect accurate odometer readings. This will not only incorrectly reflect the number of miles you've driven, it will also give you an inaccurate picture of your MPG.
 Many freeways have "mileage check sections." They are stretches of road several miles or kilometers long, with mileage markers along the way. If one near you has this feature, use it. Otherwise, look on the map and find a stretch of road or freeway, and mark out an accurate 5 or 10 mile (or kilometer) distance.

2Go to the first marker. Set your trip odometer to 0 as you pass the marker.
 At the end of the run, note your trip odometer. An accurate odometer will reflect the distance you traveled.
 If your odometer is higher than the distance traveled, your fuel efficiency will be better than you had calculated. You actually traveled further than you calculated with just the straight odometer reading. Conversely, if your odometer is lower than the actual distance traveled, your MPG is lower as well.

3Calculate the offset. We will call the actual distance traveled "A," and the miles shown on the trip odometer "T". We'll call offset "O." The formula for determining the offset is:
 O=A÷T.
 For example, if you travel 5 miles, and your odometer says you've traveled 41/2, your formula would read:
 O = 5÷4.5; O=1.11. To get your actual mileage for your MPG formula, you would subtract Mileage A from Mileage B as normal, then multiply the result by 1.11 before finishing your MPG calculation.
 If Mileage B  Mileage A = 100, multiply by O (1.11). In this example, you actually traveled 111 miles.
 If your odometer says you traveled 51/2 miles, your formula would read:
 O=5÷5.5; O=.91. Again, you would multiply Mileage B  Mileage A by O.
 If Mileage B  Mileage A = 100, multiply by O (0.91). In this example, you only traveled 91 miles.
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Community Q&A

QuestionI have put 30 litres of petrol in my car, and I have done 375 miles. How many miles am I doing to the gallon?Community AnswerAssuming you USED exactly 30L to travel 375 miles. U.S. Gallons is 47.3 MPG, UK Gallons is 56.8 MPG.

QuestionI filled my car up, and it says that I am now using 9.3 per 100 litres. What does this mean?Community AnswerIt must be saying 9.3 per 100km; it means as per current driving conditions your car is covering 10.75km by consuming 1 liter of gasoline.

QuestionIf the fuel is listed in liters, how do I convert it to gallons?Ninja17Community Answer3.8 liters is right around a gallon, and one liter is around .26 gallons. So either way, you could just use a calculator to estimate.
Video
Tips
 You can use the MPG to experiment with ways to increase fuel efficiency. For example, if you normally drive at an average of 70 MPH, then after calculating your MPG, try driving at 55 MPH and measure your MPG again  you'll probably see it go up.Thanks!
 Try calculating your MPG more than once to get a more accurate measurement. If you did more highway driving than normal, then your MPG will be a little higher. On the flip side, if you did a little extra city (stop and go) driving, your MPG will be lower.Thanks!
 The vast majority of cars will be equipped with a trip odometer  this is a gauge that counts mileage and can be reset. This gauge is in addition to the regular odometer, which counts the number of miles a car is driven overall. One can use this to count mileage. Divide the total miles run on a full tank of fuel by the capacity of the fuel tank to obtain the mileage of the car.Thanks!
 To determine how a change in gas prices will affect your budget, take the number of miles you expect to drive in a week (or a month, or a year) and divide it by your MPG. Then multiply that answer by the price of gas per gallon. By plugging in different prices, you'll see how much more  or less  you end up paying per week (or per month, or per year).Thanks!
 To make the most of your fuel, drive between 3060 mph.^{[5] X Research source } Not only will you be paying less in fuel costs, but you will also be extending the life of your vehicle and its parts.Thanks!
Warnings
 Calculations may not be exact. Repeat these steps 23 times and average the values to get a more accurate MPG.Thanks!
 Mileage will vary with different driving patterns, the less braking and acceleration will lead to better mileage. You will see higher mileage when taking highway trips than you will after a week of driving back and forth to work on city streets.Thanks!
 In other countries, the equivalent is in kilometres per litre (km/l). In the United Kingdom, fuel is sold by the litre but fuel consumption is given in miles per gallon. To work out this calculation, times the fuel amount in litres by 0.22 (e.g. 15L X 0.22 = 3.3 gallons).Thanks!
References
 ↑ https://learn.eartheasy.com/guides/howtocalculategasmileage/
 ↑ https://learn.eartheasy.com/guides/howtocalculategasmileage/
 ↑ https://www.aa.co.za/insights/howtocalculateyourcarsfuelconsumption
 ↑ https://drivingtests.org/beginnerdrivers/howtocalculategasmileage/
 ↑ https://learn.eartheasy.com/guides/fuelefficientdriving/
About This Article
To calculate your car's fuel efficiency, start by filling up your gas tank. After you fill up the tank, record your car's mileage before you do any driving. Then, drive your car normally until the gas tank is less than half full. Once the tank is low, fill it up again and write down how many gallons of gas it took to fill it up. Also, write down your car's new mileage before you leave the pump. Finally, use the formula: miles per gallon = (mileage B  mileage A) ÷ gallons to calculate how many miles your car gets per gallon. If you want to learn how to account for an offset on your odometer, keep reading the article!