How to Calculate the Inside Diameter Knowing the Outside Diameter of a Tank

Tanks, whether for water or fuel, can only hold so much, requiring constant refilling as they run out. To determine when you'll need to start re-filling a tank, you must know what the capacity is. Measuring the inside diameter of a tank isn't always possible. But you can still determine the volume by using the outside diameter of the tank and the tank's thickness.

Measuring tape
Calculator

Instructions

- 1
  Stretch a tape measure across the top of the tank. Make sure to cross the exact center of the tank. Mark the length showing as the outside diameter.
- 2
  Measure the thickness of the water tank. Multiply the thickness by two and subtract that from the outside diameter to calculate the inside diameter of the tank.
- 3
  Use a measurement of the outside circumference of the tank if you cannot get a diameter measurement across the top of the tank. Just run the measuring tape around the body of the tank to get its circumference, making sure to keep the tape level all around.
- 4
  Divide the circumference by 3.1415 to get the tank's outside diameter. Measure the tank's thickness, multiply by two and divide the results from the outside diameter to calculate the inside diameter.

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