How to Find Out the Capacity of Your Gas Tank

by Soren BagleyUpdated August 14, 2023
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There are many reasons for wanting to know your gas tank capacity or the miles per gallon (mpg) your car gets at full capacity. One of the most common reasons people want to find out this information is that they believe the gas station is charging them for too much gas to fill their fuel tank at the gas pump. Another reason is that people may want to calculate the number of fill-ups and amount of fuel they need for a road trip. Others may worry that their fuel economy is draining because of a problem with their fuel efficiency or vehicle. Because the gallons of fuel your vehicle needs greatly depends on the type of car you have (for instance, a Ford F-150 truck vs. a small Toyota car vs. an SUV will have very different fuel consumptions and gas mileage), it can be difficult to ‘guesstimate’ your vehicle’s fuel tank. Whatever your reason for wanting to find out your fuel tank capacity, the process is very simple.

1. Check your owner's manual

Check your owner's manual. The owner's manual will always list specs like the average capacity of a gas tank for your specific model and make of car. However, be aware that this number is still only an estimate and can vary from the actual tank capacity by as much as three percent.

2. Measure your gas tank size

Measure your gas tank size. To do this you will need to get under the car and physically measure the size of your tank with a tape measure. Measure the height, width and length of the tank in inches. Once you have the measurements, go to the URL and enter the data into the appropriate fields. Click "calculate" and the site will provide you with your tank capacity in gallons.

3. Run your tank completely out of gas and then see how much fuel it takes while refueling

Run your tank completely out of gas and then see how much fuel it takes while refueling. The best way to do this is to first fill up a 1-gallon container of gas at the gas station. Keep the gallon of gasoline in your car while you drive around, preferably already at very low fuel. Drive until your car is completely out of gas, making sure that a gas station is nearby when you run out. Pour the gallon of gas into the tank and drive the rest of the way to the gas station. Pump gas from the fuel pump at the station into your tank until your tank is full. The number of gallons that it takes to fill up your tank is the capacity of your tank minus one gallon or less (the fuel level that was in the container).


The average gas tank holds 15 to 18 gallons of gas.

Video: How to Measure the Amount of Oil in Your Tank

Helpful comments on this video:

  • Actually my fuel tank is protected with a lot of wired meshes which doesn't allow the measuring tape to go inside. Any other alternative method for measuring
  • Won't work. Tank is not the same size at the lower level.

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