Aquarium Calculator - Calculate Fish Tank Volume

It is important to know the your aquarium size so that you can figure out what fish you can keep in it. Ideally, you have researched your fish first and then picked your tank size to meet their needs.

In your research you will come across articles written by people using a different measuring system than you (english or metric) and the converters on this page can quickly help you perform these conversions.

There are several calculators on this page and you can use the quick links below to jump to the one you need.

Quick Jump Menu:

Rectangle Fish Tank Volume in Gallons

rectangular aquarium volume calculator
Aquarium volume is:
Next: Get Fish Stocking Suggestions for aquariums this size.

Cylinder Aquarium Volume

cylinder aquarium size calculator
Aquarium volume is:

For cylinder style aquarium stocking ideas: 3 Gallon Cylinder ideas?


Hexagon Aquarium Volume

hexagon aquarium size calculator
Aquarium volume is:

For hexagon stocking ideas: Fish that do well in a hexagon tank


Fishless Cycle Ammonia Calculator

new tanks would be at 0 ppm

4 or 5 ppm is good to start cycling

(convert liters to gallons)

ammonia strength % is on the bottle label

mL or drops of pure ammonia (1ml = 20 drops)
Be sure to check out the aquarium cycle article for more details and tips on fishless cycling!


Heater Size

*Always unplug heaters before working on your aquarium! Please note that these heater size recommendations are approximations. Tank wall thickness and whether or not you use a lid or top on your aquarium could affect the heater size needed.


Chiller Size


*The formula used for calculating aquarium chiller size is: volume in gallons * 8.34 weight of 1 gallon of water * temperature pull down needed * 20% padding factor. It's better to use an oversized chiller (hence the 20% padding factor in the calculation) than an undersized one to ensure it lasts longer and doesn't have to work as hard and other factors that could impact the efficiency of the unit such as ambient room temperature.


Fahrenheit to Celsius


Celsius to Fahrenheit


Gallons to Liters


Liters to Gallons


Inches to Centimeters


Centimeters to Inches


UK Gallons to US Gallons


US Gallons to UK Gallons


Meters to Feet


Feet to Meters


Meq/L to dKH CaCO3 (ppm)



dKH to Meq/L and CaCO3 (ppm)


CaCO3 (ppm) to Meq/L and dKH


Recent Forum Discussions:


Site References :
Wikipedia - for some of the formulas used.

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