The Fuel in a 268 Gallon Tank calculator computes the content volume in a 268 gallon above ground storage tank (AST) based on the tanks standard dimensions and the measurement of a dipstick (see Directions). 
Above ground Storage Tank
INSTRUCTIONS: Choose units and enter the following:
- (D) Depth of Liquid in Tank (wet dipstick)
Volume (V): The calculator returns the volume of fuel in the tank in gallons. It also returns the volume of fuel needed to fill the tank in gallons. However, these can be automatically converted to other volume units (e.g. liters, barrels) via the pull-down menu.
The Math / Science
This calculator answers the question, "How much is in my 268 gallon fuel tank?"
268 gallon fuel tanks have standard dimensions of 60" length, 27" width and 44" height. Based on these dimensions, one can calculate the total volume. To compute the volume of liquid in the tank, enter a dipstick and measure the depth of the liquid (D).
ASTs are used for home heating oil, kerosene and diesel fuel.
The typical AST has a cap that is used to refuel the tank. This is the easiest place to insert a dipstick (measuring stick) to measure the depth (D) of the liquid content of the AST. 
Above ground Storage Tank with diesel fuel
These pictures show an above ground storage tank with diesel fuel with a hand crank that pumps 10 gallons for every 100 turns of the pump crank(See Hand Pump Volume formula). During cold periods, the fuel supplier will treat the diesel with an anti-freeze mixture, but this is only a concern if the temp is well below zero degrees F (e.g.-5 F or colder).
Test
The tank in the picture has a factory label indicating a 266 gallon capacity. It was installed at my farm by the good folks at Bruceton Petroleum. The dimensions are 60" long (l), 27" wide (w), and (43 3/4") high (h). If you enter a dipstick reading (d) equal to the height (43 3/4"), the algorithm produces 266.02 gallons.
Storage Tank Calculators:
- Storage Capacity of a Rectangular Tank
- Above Ground Storage Tank Capacity
- Storage Capacity of a Horizontal Cylindrical Tank
- Fuel in a 268 Gallon Tank
- Fuel in a 322 Gallon Tank
- Fuel in a 150 Gallon Circular Tank
- Fuel in a 270 Gallon Circular Tank
- Fuel in a 525 Gallon Circular Tank
- Fuel in a Skid Tank
- Fuel in a 300 Gallon Skid Tank
- Fuel in a 550 Gallon Skid Tank
- Fuel in a 1000 Gallon Skid Tank
- Fuel in a 1500 Gallon Skid Tank
- Fuel in a 2000 Gallon Skid Tank
- Fuel in a 2500 Gallon Skid Tank
- Volume of a Torispherical Head
- Volume of a Torispherical Tank
- Hand Pump Volume: Computes the number of cycles (pumps or cranks) needed to move a specified volume
- Volume from Pump Rate over Time: Computes gallons pumped or consumed based on a rate and time duration.