Calculate gallons per inch and tank volume by liquid level for vertical cylinders, rectangular tanks, or horizontal cylinders with reverse depth solving.

Internal dimensions; uniform tanks with flat ends. Horizontal gallons per inch varies with depth.

Liquid weight (optional)

Leave blank to omit liquid weight.

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Gallons Per Inch Formula

The following formula is used to calculate gallons per inch for a uniform vertical cylindrical tank. Horizontal cylinders require circular-segment geometry because volume per inch changes with depth.

GPI = π × (D / 2)² / 231; gallons = GPI × H

Variables:

  • GPI is the gallons per inch
  • D is the diameter of the tank (inches)
  • H is the height of the liquid in the tank (inches)

For a vertical cylinder, divide its circular cross-sectional area in square inches by 231 to find US gallons per inch. Multiply by liquid depth H to find total gallons. One US liquid gallon equals 231 cubic inches.

What is Gallons Per Inch?

Gallons per inch is a measure of the volume of liquid that occupies a one-inch height in a cylindrical tank. It is a useful metric for determining the amount of liquid in a tank based on the liquid level’s height. This measurement is particularly important in industries where precise volume measurements are necessary, such as in chemical processing or water treatment facilities.

How to Calculate Gallons Per Inch?

The following steps apply to a uniform vertical cylindrical tank. Select the corresponding mode for rectangular or horizontal tanks.

  1. First, measure the diameter of the tank (D) in inches.
  2. Next, measure the height of the liquid in the tank (H) in inches.
  3. Use GPI = π * (D/2)^2 / 231 to calculate US gallons per inch.
  4. Finally, multiply GPI by H to find the liquid volume in US gallons.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem :

Use the following variables as an example problem to test your knowledge.

Diameter of the tank (D) = 36 inches

Height of the liquid in the tank (H) = 1 inch. GPI = π × 18² / 231 ≈ 4.4064 US gal/in, so the liquid volume is approximately 4.4064 US gallons.