AQUARIUM DIMENSIONS: Sizes + Calculations

Aquarium dimensions and overall aquarium sizes may vary depending on the manufacturer’s calculation. When you buy a tank the actual aquarium dimensions of one brand of the tank may be larger or smaller than the aquarium dimensions for the same gallon tank size.  Even the trim type or color may change the aquarium dimensions of a tank.

Aquarium Dimensions: Take Inside Measurements

You should always measure the tank size, do not just follow the label on the box or the store marketing information.  Remember the inside of the tank is the water volume – not the outside.  Measure inside the glass or acrylic so that you are not allowing for the thickness of the walls when you are working out how much water it will hold…

You know that sometimes items are returned to a store, put into the wrong box, and then resold.  Always better to measure and check before leaving the store.

Typical Store and Online Fish Tank Sizes

If you have the aquarium size already, maybe buying online, the following will help you check the water size in US gallons or liters. Remember the overall outside size of the tank will be bigger allowing for the glass thickness.  For example, a small aquarium may have glass that is 1/8 of an inch, whereas a larger tank may need glass 3 /4 of an inch thick.

For the actual tank size use our aquarium calculator here.

How much water will the fish tank really hold?

Theoretical volume

This is the absolute volume when an otherwise empty tank is filled to the very top edge with water.  This is the size that the manufacturer will often state.

Realistic volume

Allows for decor displacement and that the tank won’t be filled to the very top edge. As such this is a far more accurate measurement to use.

How high you fill the water and what you place in the tank will decrease the amount of water volume to a more realistic lower quantity.  For example, a small 2.5 Gallon tank 12 x 6 x 8 holds 2.5 Gallons when completely full to the top.  But allowing for the water to be lower than the very top rim, some plants and decorations in the tank the actual realistic volume is more likely to be 2.25 Gallons. 

The following table provides typical fish tank dimensions for the most commonly available unless you buy a custom made.

TYPICAL AQUARIUM DIMENSIONS

All measurements are for the INSIDE of the tank. 

These are ‘Theoretical Volumes’

Aquarium Dimensions: Sizes Under 100 Gallons

Aquarium Dimensions: Sizes Over 100 Gallons

For the actual tank size use our aquarium calculator here.

There are other types of tanks such as bow front tanks, hexagon, and round tanks as well as bespoke made-to-measure shapes.  It is important to plan your tank allowing for the space it will occupy, ensuring plenty of room for access and cleaning around the tank, the stand, and all the equipment.

Aquarium Weight

Below is an estimate of aquarium weights comparing empty to full, saltwater, or freshwater. 

The weights are an estimate because the amount of rock, planting, and thickness of glass are assumed figures.
For planting and rocks, anything other than fish is shown so that you can see what we have assumed.

How Much Does a Gallon of Water Weigh?

A gallon of freshwater at 39.2ºF, or 4ºC, and a specific gravity of 1.000 weighs 8.3454 lbs. 

The weight of the water will increase directly proportionate to the weight of the salt being dissolved in the water. 
1 gallon of water 8.3454 lbs times the specific gravity of say 1.025 equals 8.5540 lbs (8.3454 x 1.025 = 8.5540).

1 gallon of saltwater at 1.025 specific gravity equals 8.554 lbs.

For more details on ‘how much a gallon of water weighs see our post here

For your own tank, you decide how much planting etc will be added and alter the weights to suit your needs.

Please download Our ‘Aquarium Dimensions, Sizes & Weights’ booklet for your future reference: