Tank measurement charts are available that show the size of the tank, the fuel capacity and how to gauge the amount of fuel in the tank. The charts are used for home heating fuels, large capacity fuels and propane. Companies such as 21st Century Energy post them on their websites.
Using the home heating fuel chart as an example, the first entry is for a horizontal tank with a capacity of 275 gallons. Its dimensions are 27 inches wide, 44 inches in diameter and 60 inches in length. The first column marks off the inches. The column under the horizontal tank shows the number of gallons of fuel oil each inch holds. If the tank gauge measures 10 inches of oil left, that means 96 gallons are available.