Calculating the capacity of a gas tank requires measuring the dimensions of the tank. If the tank is not accessible, it might be considerably easier to look at the specifications for your automobile on the manufacturer website, although this will likely be an estimate. You can also run the tank dry and refill it, which will tell you the exact, usable capacity. However, if you have access to the tank, calculating the total volume would be easier than the latter option.

- Skill level:
- Moderate

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### Things you need

- Tape measure

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## Instructions

- 1
Measure the length, width and height of the gas tank. The height should be measured to the top off the main tank. If you notice a separate bulbous protrusion at the top of the tank, that is the vapour head space, which will not contain gas, so only measure the height of the main body of the tank, usually where the filler pipe enters the tank.

- 2
Use the volume formula: volume = length * width * height.

- 3
Enter your measurements. As an example, if you measured a tank 24 inches by 24 inches by 8 inches, you would calculate:

Volume = 24 inches * 24 inches * 8 inches

Volume = 4,608 cubic inches

- 4
Convert cubic inches to gallons by dividing by 231. In the example, 4,608 cubic inches divided by 231 would give you 20 gallons (rounded).

- 1
Measure the height and diameter of the gas tank in inches. If the tank is horizontal, use the length will instead of the height.

- 2
Divide the diameter measurement by two to calculate the radius.

- 3
Use this formula: volume = pi * radius squared * height. Pi is a constant measured as 3.14.

- 4
Plug in your measurements to calculate volume. As an example, say you measured a length of 24 inches and a radius of 8 inches.

Volume = 3.14 * 10 inches * 10 inches * 36 inches

Volume = 11,304 cubic inches

- 5
Convert to cubic inches to gallons by dividing by 231. In the example, 11,304 cubic inches divided by 231 would give you 49 gallons (rounded).