When it comes time to add medication or stock fish, it is essential to know the volume of your aquarium. The same is true when doing a partial water change. Aquarium tanks typically are labelled according to the tank size. They could be 10, 20, or 55 gallons, however, this is the outside tank size, which differs from the water volume that the tank holds. To ensure the proper treatment of the aquarium, calculate the water volume, making a 10 to 20 per cent allowance for various decorations in the tank.

Measure the length of the tank. Start at either the front or back panel, and measure the distance from left to right. For the most accurate calculation, all measurements should be taken from inside the tank.

Measure the height of the tank (top to bottom), and then the depth (front to back).

Multiply the three measurements, length, height and depth, to calculate the cubic inches.

Calculate the volume of the tank by multiplying the cubic inches by 0.00433.