How Much Does a 20 Gallon Fish Tank Weigh With Water?

If you’re considering setting up a 20-gallon fish tank, you might wonder, “how much does a 20 gallon fish tank weigh with water?”. The answer is straightforward: A 20-gallon aquarium will weigh approximately 225 pounds when filled with water.

This includes the weight of the water, the tank, and any decorations or substrate you may have added to the tank. It’s important to consider this weight when deciding where to place your fish tank, as it will need to be situated on a sturdy and level surface that can support the whole weight.

Let’s keep reading to have a more accurate answer.

How Heavy is a 20 Gallon Fish Tank With Water?

How much does a full 20 gallon fish tank weigh?

The 20 gallon tank weight with water can vary based on several factors including the measurements of a 20 gallon tank, tank’s material, as well as whether the water is saltwater or freshwater.

Let’s clarify each factor to get the most accurate answer for 20 gallon aquarium weight.

1: Tank’s dimensions

Type of 20-gallon tankEmpty tankFull water
High tank (24″ x 12″ x 16″)25 pounds225 pounds (102 kg)
Long tank (30″ x 12″ x 12″)25 pounds225 pounds (102 kg)


  • Long tank: For a 20-gallon-long fish tank, which typically measures 30L” x 12W” x 12H”, the weight with water can reach around 225 pounds.
  • High tank: If the 20-gallon fish tank is a high tank, which usually measures 24L” x 12W” x 16H”, it will weigh approximately 225-250 pounds when filled with water.

This weight can also vary depending on the weight of any substrate or decorations in the tank, so it’s essential to use a sturdy stand that can support the weight and its contents.

2: Tank’s material + Type of water

Tank MaterialSaltwaterFreshwater
Glass tank181 pounds (82 kg)177 pounds (80 kg)
Acrylic tank171 pounds (77.5 kg)167 pounds (75 kg)
  • Glass tank with freshwater: The weight of the glass tank and water combined will be around 177 pounds (80 kg). This includes the tank’s weight, which is typically around 25 pounds (11 kg), and the weight of the freshwater, which is around 8.34 pounds (3.78 kg) per gallon.
  • Glass tank with saltwater: The total weight of the tank combined with the weight of 20 gallons of water will be around 181 pounds (82 kg). Saltwater is denser than freshwater which is about 8.6 pounds (3.9 kg) per gallon. That’s why the tank with saltwater will be heavier.
  • Acrylic tank with freshwater: The weight of the tank plus the 20 gallon water weight will be around 167 pounds (75 kg). 20-gallon acrylic tanks are typically lighter than glass tanks which are about 10 pounds (4.5kg).
  • Acrylic tank with saltwater: The total weight of the acrylic tank and saltwater combined will be around 171 pounds (77.5 kg). It’s important to know that saltwater is generally heavier than freshwater because of the dissolved salts and minerals in it.

Weight of Custom-shaped Tanks Calculation


As long as the tank’s volume in gallons is specified, calculating a 29 gallon or 15 gallon tank is not a matter. What if you don’t know the tank’s dimensions, how to estimate its weight?

Fish tanks come in all shapes and sizes, from basic rectangles to more complex such as hexagons, or cylinders. While the volume of a tank in gallons may be predetermined for some shapes, it can be more challenging to determine the weight of a custom-shaped aquarium.

Here is the step-by-step guide to estimating the weight of a custom-shaped fish tank:

Calculating the Volume of the Fish Tank in Cubic Inches

If you’re unsure of the gallon capacity of your fish tank, determining its weight will require calculating the volume of the tank in the tank’s cubic inches first. To do this, you need to follow this formula:

231 cubic inches = 1 gallon of water

The easiest way to estimate the number of cubic inches of an aquarium is to determine how many square inches the base shape of the tank is. Then multiply the result by the tank’s height.

The next step is to divide the total cubic inch volume that you just found by 231 to figure out the tank’s gallon.

However, it’s easier said than done, not all people are able to figure out the tank’s base shape. Let’s break down the calculation

  1. Place the fish tank on a piece of paper and draw around the bottom of the tank. If it’s a hexagon or another complex shape, divide it into triangles, squares, or any other cubes that can be measured easily with math.
  2. Determine the area of all shapes (inches) and add up the areas of all shapes to find the total area of the bottom of the tank.
  3. Take that result and multiply it by the tank’s height to find the aquarium tank volume in cubic inches.
  4. Divide that volume you just found above by 231 to calculate the number of gallons.

Estimating the Weight of a Fish Tank

Once you know how many gallons your tank is, you can estimate its weight. The weight of water is approximately 8.34 pounds per gallon. Therefore, you can multiply the fish tank’s gallon by 8.34 to estimate the weight of the tank.

For example, if you have a custom-shaped tank with a base area of 400 square inches and a height of 20 inches, the fish tank’s volume would be:

400 x 20 = 8,000 (cubic inches)

Dividing this number by 231 gives you a gallon capacity:

8000: 231= 34.63 (gallons)

Multiplying the gallon of the aquarium by 8.34 gives you an estimated tank weight:

34.63 x 8.34 = 288.67 (pounds)

Calculating the weight of a tank may seem daunting, but it’s a crucial step in ensuring that your tank is safely supported. With this guide, you can calculate the weight of any custom-shaped aquarium accurately.

Frequently Asked Questions


How much water does a 20 gallon fish tank hold?

A 20 gallon fish tank holds approximately 20 gallons of water. Knowing the weight of a gallon of water, which is approximately 8.34 pounds, we can answer the question “how many pounds is 20 gallons?”.

The weight of water in a 20-gallon fish tank multiple with 8.34 is about 166.8 pounds.

However, this weight can vary depending on the type of substrate and decorations in the tank, as well as the weight of the type of the tank. It’s important to consider the weight of the filled tank when deciding where to place it, as it can be quite heavy and require a sturdy stand or surface.

Is a 20 gallon aquarium big?

A 20 gallon fish tank is not a big-sized tank. However, it’s an ideal size for small fish families or those fish that require their own tank due to their territorial nature.

It’s important to keep in mind that overcrowding should be avoided in this medium tank, as this can lead to poor water quality and health problems for the fish.

While a 20 gallon aquarium tank can have different types of fish species, it may be too small for some larger species or those that produce a lot of waste. In comparison, a bigger tank like a 55 gallon aquarium offers more space and can support a wider variety of fish species, but requires more maintenance.


How much does a 20 gallon fish tank weigh with water? A 20-gallon fish tank weighs approximately 225 pounds when filled with water.

It is crucial to know that the aquarium’s weight does not include the weight of any decorations, gravel, or fish. Therefore, it is always advisable to calculate the weight of the fish tank and its contents to ensure that your chosen location can safely support the weight.