Calculate the True Volume of Your Fish Tank

Posted on June 08 2024, By: Aquarium Dimensions

Aquarium fish tank water volume calculator

Aquarium Dimensions Volume Calculator

Step 1) Measure the length, width, and height dimensions of your aquarium.

Step 2) Enter each fish tank dimension into the calculator. Don't forget to enter inches, centimeters, feet, etc.

Step 3) Estimate or measure how much room is left between the water level and the top of the tank.

Step 4) Calculate!

Tank Volume Calculator


Estimate How Much an Aquarium Will Weigh When Filled

If you would like to calculate the weight of your aquarium, remember that water weighs about 8.34 pounds per gallon.

Don't forget about the weight of the aquarium itself and everything else you will be putting in it such as gravel or rock.

Glass aquariums start at around 11 pounds empty for a 10 gallon, all the way up to 400 pounds empty for a 265 gallon!

Factors Affecting Fish Tank Volume Calculation

Many additional factors can affect the volume of a fish tank, even though it is primarily determined by the aquarium’s dimensions. 

Substrate Layer

The amount of substrate you add to an aquarium can affect the fish tank’s volume. If you add a 1-inch thick layer of a substrate to a 10-inch tall aquarium, you are approximately reducing its volume by 10%. Increasing the substrate layer to two inches will reduce the water volume by 20% to 8 gallons.

However, it also does depend on the type of substrate being used. Fine substrates like sand will reduce the volume by 10%, but gravel may have a slightly less impact on the volume of water (6-7%). Therefore, be mindful of how much substrate you are adding to an aquarium. Consider a fish tank with a large volume if you want a thick substrate layer.

Decorations and Items

Decorations and items like trees, houses, air stones, and internal power filters will occupy space in the aquarium. As you add more items, it will lower the fish tank’s volume and the amount of water it can hold. One or two small decorations may not hurt, but if you are planning to build an underwater castle for your aquatic pets, opt for a slightly larger fish tank. Internal power filters may occupy a lot of space as well. If you will use one such device, consider its impact on the fish tank’s volume. Compensate for the same by buying a fish tank with more volume.

Fish Tank Volume Calculation and Overpopulated Aquariums

fish tank volume calculator prevent overcrowding

You must avoid overpopulating aquariums with inanimate objects. It is especially crucial for aquariums that are small in size, under 10 gallons. You may think that the tank has a capacity of ten gallons and will be adequate for a particular species of fish. However, if you overpopulate it, it may only be able to hold 7 to 8 gallons of water in reality. It may not be adequate for the aquatic life in the tank.

Filtration for Fish Tank Volume

fish tank volume calculator proper filtration

The power or canister filter must also have a higher flow rate to clean water in a 7-gallon tank compared to a 10-gallon tank. Otherwise, the water may not be cleaned at an adequate rate. While you may not notice any sudden changes in the aquarium, it will gradually impact the aquatic life. It may be detrimental to the health of the fish and plants in the tank. The lifespan of the pump may degrade, and its filtration media may have to be replaced more frequently. Therefore, it is crucial that an aquarium must not be overpopulated with either fish, plants, or decorations. Choosing the right fish tank volume for your requirements becomes essential.

Manufacturers Fish Tank Volume

Quite a few manufacturers account for objects like decorations and gravel in their aquarium specifications. The fish tank’s actual volume may be 11 or 12 gallons, but the seller may only list it as 10-gallons. Check if the manufacturer states the exact volume of a fish tank or leaves some leeway for gravel, plants, decorations, and other items that you might add to the aquarium.


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