Volume is the measurement of how much liquid a container can hold. It is important to know the volume of a fish tank when setting up the tank and obtaining fish because each fish requires a different amount of space in the tank. If you miscalculate your total volume for the fish, it could result in territorial disputes and mortality.
Measure your tank's height, length and width using a measuring tape and write these numbers down. The height is from the top of the tank to the bottom. The length is from right to left and the width is from front to back.
Multiply the numbers together using your calculator to get the total volume in square inches.
Multiply that number by .00433 to get the number of gallons your tank holds.
Multiply this number by 3.7854 to get the number of litres your tank holds.
For those who don't want to calculate this by hand, use the volume calculating program in the resource section.