The heating fuel oil tank chart below is an estimate of the amount of gallons in your tank. Use a tank stick to measure the inches of oil currently in your tank then match up the inches with the size of your oil tank that corresponds on our chart below. To accurately measure how much heating oil you’ll need first you must know the size of your fuel tank. Once you have your tank size, you only need to refer to that down column on the chart. Next, insert your oil tank measuring stick to show the inches of oil left in your tank. This will now indicate whether your tank is low and needs to be filled, or if you are good for another few weeks. For example, if you have a 275 horizontal tank and the measuring stick is reading a depth of 5” it is time to buy heating oil.