How to calculate the volume of an aquarium?

To calculate the volume of a rectangular aquarium, multiply its length, width and height. For round or angled tanks, multiply the base area by the height. This tool will apply the appropriate formula based on your shape selection and convert the result to gallons or liters.

Why is the actual amount of water less than the aquarium volume?

There are two reasons for this: In most cases the tank is not filled to the very top and rocks, sand and equipment take up space that would otherwise be water. By enabling the options to account for water depth and volume taken up by objects you will get a more accurate indication of how much water actually fits in your tank. This is also the value that should be used when calculating dosages of medication.

How many gallons will fit in the aquarium if it is measured in inches?

To calculate volume in cubic inches, multiply the length, width and height (in inches) together. Then divide that number by 231. One U.S. gallon is equal to 231 cubic inches. To calculate volume in liters, use centimeters to find the cubic centimeters then divide that number by 1000.

How heavy is an aquarium filled with water?

Fresh water weighs about 8.34 pounds per US gallon or almost a kilogram per liter. Saltwater weighs about 2.5 percent more. Multiply the calculated amount of water by that figure and don't forget to add in the weight of the tank itself, stand, rocks, gravel, etc.

Does the volume change depending on what type of water it is?

No, the volume is determined by the dimensions and shape of the tank. Only the weight will change depending on what type of water it contains. Saltwater is denser than freshwater. You can observe the change in weight by switching between the "freshwater" and "saltwater" options.

Aquarium Volume Calculator

Aquarium dimensions

Aquarium shape

What to measure: Measure the length, width, and height of the water space.

Length

Width

Height

Water type

Freshwater

Saltwater / reef

Not filled to the top

Enter the real water depth if the tank sits below the rim.

Account for substrate, rock and decor

Subtract the space taken by sand, rock, and equipment.

Total volume

Water weight (full)

Total volume

US gal

Water weight (full): lb
Footprint area: in²

Filled to the top this tank holds about 19.95 US gal of water, weighing roughly 166.5 lb. Check that your stand and floor can carry that load before you fill it.

Charts

The aquarium volume calculator tool converts the dimensions of an aquarium into a number that is actually important to everyday life: how much water it can hold. Select the shape of your aquarium and enter its measurements to find out the volume in US gallons, liters or UK gallons.

The volume affects almost every decision you make in an aquarium. It determines the number of fish you can keep, how much salt or lime you need to add and the amount of medication required. Also it tells you the weight of the tank when full so that you can judge if your table or floor can support this weight.

Why does the stated aquarium volume often not match what actually fits in?

An aquarium listed as "40" is only a guideline and not an actual measurement of volume. The thickness of the glass, frame, and rounded corners reduce the amount of water it holds. Even more important, you will almost never fill your tank to the very top, and rocks and substrate also take up space.

This calculator takes both of these aspects into account. When you activate "Water level height", the calculation will not start from total height but from actual water level. When you activate "Volume deduction", spaces occupied by sand, stones and equipment are deducted. The result is the actually available volume of water, which is the number that should be used when calculating medication dosages.

Measurement methods and use.

To ensure that the frame does not affect the result, measure from inside - within the glass - and not from outside. Use either inches or centimeters. A calculation tool will convert the values and show the result in the chosen unit. First select the shape, then enter the measurements required for this shape.

For a round aquarium measure the diameter that crosses the top and divide by two to get the radius. For hexagonal or curved front aquariums you will need to measure both the front panel as well as the slanted sides. A shape guide will walk you through step-by-step what to do.

Formula for calculating volume:

Since each shape treated here is an aquarium with straight walls and a constant cross-sectional area, the volume results from multiplying the base area by the height. A typical rectangular aquarium is the simplest example.

V = L \times W \times H

For a cylinder, the area of the circle is used as the base.

V = \pi \times r^2 \times H

The volume of a half-cylinder is half the above volume while that of a quarter-cylinder rectangular aquarium is one-quarter of the above volume.

V_{\text{half}} = \frac{\pi \, r^2 H}{2} \qquad V_{\text{corner}} = \frac{\pi \, r^2 H}{4}

Regardless of the shape of the container, the conversion method is always the same as long as you know the volume. One U.S. gallon is equal to 231 cubic inches and one liter is equal to 1000 cubic centimeters.

\text{US gallons} = \frac{\text{cubic inches}}{231} \qquad \text{litres} = \frac{\text{cubic centimetres}}{1000}

The weight of an aquarium filled with water

Since water is heavy, an aquarium filled with water will weigh much more than the same tank empty. Freshwater weighs about 8.34 pounds per US gallon and has a mass of nearly one kilogram per liter. Saltwater is denser and due to the salt content in a reef aquarium it will be around 2.5 percent higher, so a reef aquarium of the same size will weigh slightly more.

The table below shows the weight of water for some common sizes of freshwater aquariums.

Tank size	Water volume	Water weight (fresh)
20 gallon	20 US gal / 76 L	about 167 lb / 76 kg
40 gallon	40 US gal / 151 L	about 334 lb / 151 kg
75 gallon	75 US gal / 284 L	about 626 lb / 284 kg
125 gallon	125 US gal / 473 L	about 1043 lb / 473 kg

This only calculates the weight of the water. If you add in the aquarium, stand, rocks and substrate, then the total weight that the ground has to support is significantly higher.

The following formats are supported by this tool.

In addition to the standard rectangular and cube shapes, the program also supports cylinders, half-cylinders and quarter-cylinders, as well as oval and hexagonal aquariums, aquariums with a curved front, corner pentagon aquariums, L-shaped aquariums and triangular aquariums. For each shape, only the required dimensions need to be entered. The calculated base area can be used to estimate the coverage by lighting or to calculate the amount of substrate needed.

This tool provides geometric estimates for your planning purposes. As the actual volume will vary depending on glass thickness, frame and water level, results should be considered as guidelines rather than exact values.

Frequently asked questions

How to calculate the volume of an aquarium?: To calculate the volume of a rectangular aquarium, multiply its length, width and height. For round or angled tanks, multiply the base area by the height. This tool will apply the appropriate formula based on your shape selection and convert the result to gallons or liters.
Why is the actual amount of water less than the aquarium volume?: There are two reasons for this: In most cases the tank is not filled to the very top and rocks, sand and equipment take up space that would otherwise be water. By enabling the options to account for water depth and volume taken up by objects you will get a more accurate indication of how much water actually fits in your tank. This is also the value that should be used when calculating dosages of medication.
How many gallons will fit in the aquarium if it is measured in inches?: To calculate volume in cubic inches, multiply the length, width and height (in inches) together. Then divide that number by 231. One U.S. gallon is equal to 231 cubic inches. To calculate volume in liters, use centimeters to find the cubic centimeters then divide that number by 1000.
How heavy is an aquarium filled with water?: Fresh water weighs about 8.34 pounds per US gallon or almost a kilogram per liter. Saltwater weighs about 2.5 percent more. Multiply the calculated amount of water by that figure and don't forget to add in the weight of the tank itself, stand, rocks, gravel, etc.
Does the volume change depending on what type of water it is?: No, the volume is determined by the dimensions and shape of the tank. Only the weight will change depending on what type of water it contains. Saltwater is denser than freshwater. You can observe the change in weight by switching between the "freshwater" and "saltwater" options.

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Disclaimer: This calculator is provided for general informational and educational purposes only. Our calculators are under active development, and results may be inaccurate, incomplete, or unsuitable for your situation. Always verify the figures independently and seek advice from a qualified professional before relying on them. We make no warranties and accept no liability for any loss or decision arising from use of this tool.

References

USGS Water Science School: Water Density
Reference values for the density and weight of fresh and salt water.
Wikipedia: Gallon
Definitions of the US and imperial gallon and their conversion to cubic inches and litres.
Wikipedia: Prism (geometry)
Volume of a prism as base area times height, the basis for every tank shape here.