There are a couple of formulas you can use to figure out how many gallons a gas tank can hold. You can use these formulas to find out how many gallons other rectangular tanks can hold as well. By determining the volume of the tank in cubic inches, and then converting cubic inches to gallons, you will know exactly how many gallons the tank holds.

- Skill level:
- Easy

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### Things you need

- Tape measure
- Calculator

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## Instructions

- 1
Measure the length, width and height of the tank in inches with a tape measure.

- 2
Multiply the length, width and height to determine the volume of the tank in cubic inches. For example, 20 times 20 times 40 equals 16,000 cubic inches.

- 3
Use the conversion formula for cubic inches to gallons: multiply the number of cubic inches by 0.00432900433. (One cubic inch contains 0.00432900433 gallons.) For example, 16,000 cubic inches times 0.00432900433 equals 69.2640693 gallons.