Fish Tank Knowledge: How Much Does a Gallon of Water Weigh?

Fish Tank Knowledge: How Much Does a Gallon of Water Weigh

It can be difficult to figure out the correct amount of water to put in a fish tank, especially when dealing with measurements like gallons. For example, did you know that there are two different definitions of a gallon – one is used in the United States, and the other is used in the United Kingdom?

In this blog post, we’ll explore how much a gallon of water weighs and how it differs between US and UK gallons.

Weight of Water: US Gallon vs. Imperial Gallon

There are two different types of gallons: the US gallon and the Imperial (UK) gallon. Both have different volumes and, as a result, different weights when filled with water.

Here are the approximate weights of water for each gallon:

US Gallon:

A US gallon of water weighs about 8.34 lbs (3.78 kg) at 62 °F (17 °C). The volume of a US gallon is approximately 3.785 liters.

UK Gallon:

An Imperial gallon of water weighs about 10.022 lbs (4.546 kg) at its most dense temperature, 39 °F (4 °C). The volume of an Imperial gallon is approximately 4.546 liters.

US Gallon vs. Imperial Gallon - How Much Does a Gallon of Water Weigh

Ballpark Calculation

To simplify the understanding of water’s weight, we can use a ballpark calculation, which is an approximation that works well for most temperatures. We know that 1 liter of water has a density of about 1 kg/L. Therefore:

    1 gallon is about 3.75 liters
    1 liters = 1 kilogram (density of water is 1 kg/liter)
    1 kilogram = 2.2 lbs
    so, 3.75 kilogram is about 8.25 lbs and 1 gallon is about 8.25 lbs

      Here is a summary of the information provided and presented in a table format:

      Volume UnitTemp(lbs)(kg)Density
      1 US gallon (approx.)62 °F (17 °C)8.34 lbs3.78 kg1 kg/L
      1 Imperial gallon (approx.)39 °F (4 °C)10.022 lbs4.546 kg1 kg/L
      Ballpark Calculation (1 gallon)All temperatures8.25 lbs3.75 kg1 kg/L

      Temperature’s Effect on Water Weight: The Lighter Side of Warm Water

      💡The temperature of water has a direct impact on its weight due to changes in density. As water gets warmer, it expands slightly, and its density decreases.

      Consequently, warmer water weighs less than colder water when measured in the same volume. This principle is vital when considering the weight of a gallon of water in different temperatures.

      At 4 °C (39 °F), water reaches its maximum density of 1 kg/L. This is the temperature at which an Imperial gallon (UK) of water weighs approximately 10.022 lbs (4.546 kg).

      As the temperature increases, water becomes less dense, and its weight per gallon decreases slightly. For example, a US gallon of water weighs around 8.34 lbs (3.78 kg) at 17 °C (62 °F).

      EpicFishTank Note:

      Please remember that these values are not exact and can vary slightly depending on the actual temperature and other factors.

      Exploring the Weight of 1 US Liquid Gallon of Freshwater at Various Temperatures

      To provide a better understanding of how temperature affects the weight of 1 US liquid gallon of freshwater, we will examine the weights at different temperatures: 39.2°F (4°C), 70°F (21°C), 78°F (25.5°C), and 82°F (27.7°C).

      1. 39.2°F (4°C): At this temperature, water is close to its maximum density (1 kg/L). One US gallon of freshwater weighs approximately 8.345 lbs (3.785 kg).
      2. 70°F (21°C): As the temperature increases, the density of water decreases, resulting in a slightly lighter weight. One US gallon of freshwater weighs around 8.329 lbs (3.778 kg) at 70°F.
      3. 78°F (25.5°C): Continuing the trend of decreasing density, one US gallon of freshwater weighs about 8.321 lbs (3.774 kg) at 78°F.
      4. 82°F (27.7°C): At this temperature, the density of water has decreased further. One US gallon of freshwater weighs approximately 8.315 lbs (3.771 kg) at 82°F.

      💡These examples demonstrate how the weight of 1 US liquid gallon.

      The Impact of Water Weight on Fish Tanks

      Water weight and temperature play a significant role in maintaining a healthy and stable environment for fish in an aquarium.

      Understanding these factors is crucial for the proper management of a fish tank, as they directly influence the fish’s well-being, the functioning of the tank’s equipment, and the water quality.

      💡Water Weight:

      The weight of water in a fish tank is an essential consideration for structural support and equipment requirements. A filled aquarium can be quite heavy, so it is crucial to ensure that the surface it is placed on can withstand the total weight.

      This includes the weight of water, tank materials, gravel or sand, decorations, and any other accessories.

      For example, a 50-gallon fish tank filled with water at 70°F (21°C) would weigh approximately 416.45 lbs (188.9 kg), not including the weight of other materials.


      Aquarium heaters, chillers, and filters may be affected by the water’s weight and temperature. As water becomes warmer, its density decreases, potentially altering the efficiency of filtration systems.

      Maintaining a consistent temperature helps ensure that the equipment functions properly and contributes to a stable

      How Much Does a Gallon of Water Weigh?

      💡The weight values in this table are based on the assumption that the water is at a temperature of 62°F (17°C) and a pressure of 1 atmosphere. Actual weight may vary depending on the conditions in which the water is being weighed.

      The table below shows the weight of various amounts of water in pounds and kilogram, based on the parameter that one US gallon of water weighs 8.34 pounds (3.78 kilograms).

      1 gallon of water8.34 lbs3.78 kg
      2 gallon of water16.68 lbs7.56 kg
      2.5 gallons of wate20.85 lbs9.45 kg
      3 gallon of water25.02 lbs11.34 kg
      4 gallons of water33.36 lbs15.12 kg
      5 gallons of water41.7 lbs18.9 kg
      6 gallons of water50.04 lbs22.68 kg
      7 gallons of water58.38 lbs26.46 kg
      8 gallons of water66.72 lbs30.34 kg
      9 gallons of water75.06 lbs34.02 kg
      10 gallon of water83.4 lbs37.8 kg
      12 gallons of water100.08 lbs45.36 kg
      13 gallons of water108.42 lbs49.14 kg
      14 gallons of water116.76 lbs52.92 kg
      15 gallons of water125.1 lbs57.0 kg
      16 gallons of water133.44 lbs60.48 kg
      18 gallons of water150.12 lbs68.04 kg
      20 gallons of water166.8 lbs75.6 kg
      25 gallons of water208.5 lbs94.5 kg
      29 gallons of water241.86 lbs109.62 kg
      30 gallons of water250.2 lbs113.4 kg
      35 gallons of water291.9 lbs132.3 kg
      40 gallon water weight333.6 lbs151.2 kg
      46 gallons of water383.64 lbs173.88 kg
      50 gallons of water417 lbs189.0 kg
      55 gallons of water458.7 lbs208.5 kg
      60 gallons of water500.4 lbs227.0 kg
      65 gallons of water542.1 lbs245.5 kg
      70 gallons of water583.8 lbs264.0 kg
      75 gallons of water625.5 lbs282.5 kg
      80 gallons of water667.2 lbs301.0 kg
      90 gallons of water750.6 lbs340.2 kg
      100 gallons of water834 lbs378.0 kg
      120 gallons of water1000.8 lbs453.6 kg
      200 gallon water weight1668 lbs756.0 kg
      300 gallons of water2502 lbs1134.0 kg
      400 gallons of water3336 lbs1512.0 kg
      500 gallons of water4170 lbs1890.0 kg
      1000 gallons of water8340 lbs3780.0 k
      2000 gallons of water16680 lbs7560.0 kg

      How Long Does It Take to Fill a Fish Tank?

      💡According to federal regulations, all kitchen and bathroom faucets in the US should have a maximum flow rate of 2.2 gallons per minute (gpm) at 60 pounds per square inch (psi) water pressure.

      At a flow rate of 2.2 gpm, it would take approximately 27 seconds to fill a gallon of water.

      To fill a 20-gallon container, it would take approximately 8 minutes and 48 seconds at a flow rate of 2.2 gpm.

      To fill a 50-gallon container, it would take approximately 22 minutes and 48 seconds at a flow rate of 2.2 gpm.

      EpicFishTank Note:

      It’s important to note that these times are based on the maximum flow rate allowed by federal regulations, and the actual flow rate of your faucet may vary.

      Aquarium Dimensions and Typical Tank Sizes

      When it comes to setting up a fish tank, one of the most important factors to consider is the size and dimensions of the aquarium. Here are some common aquarium dimensions and typical tank sizes:

      Small Tanks:

      • 5 gallons: 16″ x 8″ x 10″
      • 10 gallons: 20″ x 10″ x 12″
      • 15 gallons: 24″ x 12″ x 12″
      • 20 gallons: 24″ x 12″ x 16″

      Medium Tanks:

      • 30 gallons: 36″ x 12″ x 16″
      • 40 gallons: 36″ x 18″ x 16″
      • 50 gallons: 36″ x 18″ x 19″
      • 60 gallons: 48″ x 12″ x 24″

      Large Tanks:

      • 75 gallons: 48″ x 18″ x 21″
      • 90 gallons: 48″ x 18″ x 24″
      • 105 gallons: 60″ x 18″ x 21″
      • 120 gallons: 48″ x 24″ x 24″

      Extra-Large Tanks:

      • 150 gallons: 72″ x 18″ x 28″
      • 180 gallons: 72″ x 24″ x 24″
      • 210 gallons: 72″ x 24″ x 28″
      • 240 gallons: 96″ x 24″ x 24″


      How heavy is a gallon of water?

      A gallon of water weighs approximately 8.34 pounds, which is roughly equivalent to the weight of eight medium-sized bananas.

      So, if you were to imagine carrying a gallon of water, it would feel similar to carrying a bag of eight medium-sized bananas. This analogy can be helpful in visualizing the weight of a gallon of water in a relatable and easy-to-understand way.

      How many pounds in a gallon?

      The number of pounds in a gallon differs slightly between the US and UK gallon due to the difference in their sizes.

      In the US, a gallon is equal to 128 fluid ounces and weighs approximately 8.34 pounds.

      In the UK, a gallon is equal to 160 fluid ounces and weighs approximately 10.02 pounds.

      EpicFishTank Note:

      It is important to specify which type of gallon is being referred to when discussing the weight of a gallon in pounds.

      Final Words

      The weight of a gallon of water can vary depending on the temperature and elevation. Generally, one US gallon of water weighs 8.34 pounds (3.78 kilograms).

      However, it is important to remember that when you are setting up your fish tank, it is not the weight of the gallon of water that determines the amount of space available for your fish – but rather the volume.

      So when setting up a fish tank you should always take into account how many gallons your tank can hold. Thanks for reading!


      1. | US Gallons And Imperial Gallons – Why Are They Different?
      2. | Water Density

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      Reza Darmesta Agustiar Avatar

      Reza is a digital marketer and an avid freshwater aquarist. He's been keeping fish tanks for more than 10 years and has always been fascinated by the delicate balance of life in water.

      Reza loves to share his knowledge about both digital marketing and fishkeeping with others, and he is always happy to help new aquarists get started in this rewarding hobby.

      Winahyu Drajat Wibisono Avatar

      Wibisono is a freshwater fish breeder who raises and breeds different species of ornamental fish like betta, guppy, flowerhorn, and goldfish. He has been in the business since 2018 and exports his fish to different countries. He is committed to providing high-quality and healthy fish to his customers.

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