Aquarium volume calculator

How the calculator works

Volume is length × width × height. With measurements in inches, dividing the result by 231 gives US gallons; with centimeters, dividing by 1,000 gives liters. The calculator does the conversion for you and shows both units.

Measure the outside dimensions of the tank. The calculator then estimates the gross volume (the full box) and the net volume, which is the water that actually goes in.

Gross vs net volume

The number on the box is the gross volume, and the real water volume is always lower. Three things reduce it:

• Glass thickness: thick glass on large tanks takes up a noticeable share of the inside.
• Water level: tanks are not filled to the brim; usually there is an inch or more (2-3 cm) of gap below the rim.
• Substrate and decor: 2-3 inches (5-8 cm) of substrate, rocks and wood can easily remove 10-20 % of the volume.

Use the net volume to dose medications, water conditioner and fertilizers, and to size the filter and heater. Overestimating the volume leads to overdosing.

Weight of the filled tank

Fresh water weighs about 8.3 lb per gallon (1 kg per liter). Add the weight of the glass, the substrate (sand and gravel are heavy: roughly 1.5 kg per liter of substrate, about 12-13 lb per gallon) and rocks. A 55 gallon tank can easily exceed 600 lb (270 kg) in total.

Always place the tank on a stand designed for aquariums or furniture that can bear the weight, perfectly level and on a solid floor. For large tanks on upper floors, check the floor structure and place the tank near a load-bearing wall.

Reading the results

The result gives you a realistic figure to work with. Use it in the heater and stocking calculators, compare it with the turnover of your filter (3-5 times the volume per hour) and calculate the amount of water to change each week: 20-30 % of the net volume.