Use this free aquarium volume calculator to find out how many gallons or liters your fish tank holds, plus the weight of the water, for any tank shape.
Fish tanks · gallons & litersAquarium Volume Calculator
Measure the inside of the glass for the most accurate result. Water weight excludes the tank, stand and substrate.
Our free aquarium volume calculator works out how much water your fish tank really holds. First, choose the shape and enter the measurements. Then the calculator shows the volume in US gallons, liters and UK gallons. In addition, it subtracts the space taken by gravel and decor and works out how much the water weighs.
Why You Need to Know Your Tank Volume
Knowing the exact volume of your tank helps you keep your fish healthy. For example, water conditioners, medicines and aquarium salt are all dosed by the gallon. In addition, filters and heaters are rated for a certain tank size, so the right volume helps you choose the right equipment.
However, the number on the label is often not the amount of water in the tank. Therefore, it is worth calculating the real figure.
How the Aquarium Volume Calculator Works
Overall, the calculator finds the area of the tank's base and multiplies it by the water depth. Then it converts the result into gallons or liters.
First, it works out the area of the bottom, based on the tank shape.
Then it multiplies by the height, minus the gap below the rim.
Finally, it subtracts the space taken by substrate, rocks and wood.
The formula (rectangle tank)
US gallons = Length × Width × Height (inches) ÷ 231
Aquarium Volume Calculator Examples
For example, here are three common tanks. In each case, the measurements are outside dimensions.
For instance, a standard tank measures 48 × 13 × 21 inches.
- First: 48 × 13 × 21 13,104 cu in
- Then: ÷ 231 56.7 gal
- Finally: in liters 214.7 L
When a cylinder is 18 inches across and 24 inches tall, its base area is about 254.5 square inches.
- First: 254.5 × 24 6,107 cu in
- Then: ÷ 231 26.4 gal
- Finally: in liters 100.1 L
Similarly, a popular European tank measures 60 × 30 × 36 cm.
- First: 60 × 30 × 36 64,800 cm³
- Then: ÷ 1,000 64.8 L
- Finally: in gallons 17.1 gal
Standard Aquarium Sizes Chart
Most US tanks come in standard sizes. However, their real volume is often slightly different from the name, as this chart shows.
| Tank | Outside size (L × W × H) | Full volume | Liters |
|---|---|---|---|
| 10 gallon | 20 × 10 × 12 in | 10.4 gal | 39 L |
| 20 gallon long | 30 × 12 × 12 in | 18.7 gal | 71 L |
| 20 gallon high | 24 × 12 × 16 in | 19.9 gal | 76 L |
| 29 gallon | 30 × 12 × 18 in | 28.1 gal | 106 L |
| 40 gallon breeder | 36 × 18 × 16 in | 44.9 gal | 170 L |
| 55 gallon | 48 × 13 × 21 in | 56.7 gal | 215 L |
| 75 gallon | 48 × 18 × 21 in | 78.5 gal | 297 L |
| 125 gallon | 72 × 18 × 21 in | 117.8 gal | 446 L |
Sizes vary slightly by brand. Also, the water volume will be lower once you allow for the glass, the rim gap and decor.
Tank Shape Formulas
- Rectangle: first, multiply the length, width and height.
- Cylinder: similarly, use 3.14 × radius × radius × height, where the radius is half the diameter.
- Hexagon: likewise, use 2.6 × side × side × height, for a tank with six equal sides.
- Corner tank: in this case, use 3.14 × side × side × height ÷ 4, because it is a quarter of a circle.
- Bow front: the calculator adds the curved front to the rectangle part. As a result, the figure is a close estimate rather than an exact one.
How Much Does a Full Aquarium Weigh?
According to the US Geological Survey, a gallon of fresh water weighs about 8.33 pounds at room temperature. In contrast, saltwater is slightly heavier, at about 8.5 pounds per gallon. Consequently, a 55 gallon tank holds about 450 pounds of water. Once you add the glass, gravel and decor, the total can be 25% higher, so always use a stand made for aquariums.
How to Use the Aquarium Volume Calculator
- First, choose your tank shape and units.
- Next, enter the length, width and height, or the diameter for round tanks.
- Then set the gap below the rim, since about 1 inch is normal.
- After that, enter the space taken by substrate and decor. Usually, 10% is a good estimate.
- Finally, choose fresh or saltwater and press Calculate Volume.
More Handy Calculators
These tools also help with measurements around the home. Alternatively, browse all our everyday calculators.
Aquarium Volume Calculator FAQs
How do I calculate the gallons in a fish tank?
First, multiply the length, width and height in inches. Then divide the result by 231, because one US gallon is 231 cubic inches. For example, a 30 × 12 × 12 inch tank holds about 18.7 gallons.
How do I calculate aquarium volume in liters?
Measure the tank in centimeters and multiply the length, width and height. Then divide by 1,000, since one liter is 1,000 cubic centimeters. For instance, a 60 × 30 × 36 cm tank holds 64.8 liters.
Why is my tank smaller than its label says?
Tank sizes are usually based on outside measurements and a full tank. However, the glass, the gap below the rim and your gravel and decor all reduce the real amount of water.
How much does a full aquarium weigh?
Fresh water weighs about 8.33 pounds per US gallon. As a result, a 55 gallon tank holds about 450 pounds of water alone. With glass, substrate and decor, the total can be 25% higher.
Why does the actual water volume matter?
Medicines, water conditioners and salt are dosed by the volume of water. Therefore, using the full tank size instead of the real water volume can lead to overdosing.
Does this aquarium volume calculator work for ponds?
Yes, for ponds with straight sides and an even depth. In other words, use the rectangle or cylinder shape. Even so, for ponds with sloping sides, the result will only be a rough estimate.
Disclaimer: This calculator gives an estimate for general information only. Tank sizes vary by brand, and glass thickness affects the real volume. Moreover, always follow the dosing instructions on any product you add to your aquarium.