How to use the aquarium volume calculator
- Choose the tank shape.
- Measure the inside length, width and water height.
- Press Calculate.
Worked example
A rectangular tank measuring 100 cm long and 40 cm wide, filled to 50 cm.
- Tank shape
- Rectangular tank
- Length (diameter for a round tank)
- 100 cm
- Width (rectangular tanks)
- 40 cm
- Water height
- 50 cm
- Litres
- 200 L
- US gallons
- 52.8 gal
- UK gallons
- 44 gal
This is the full-tank volume. Gravel, rocks and decorations displace water, so the water you can pour in is lower.
Example values are illustrative; this result is produced by the same calculator above.
How we calculate it
Sources: Pure arithmetic / unit conversion on user inputs (no external constant)
Understanding your result
A tank's volume is its length times its width times its height. Measured in centimetres and divided by 1,000, that gives litres. A tank 100 cm long, 40 cm wide and filled to 50 cm holds 200 litres.
For a round tank the calculator uses the circle formula: π times the radius squared times the height. One US gallon is 3.785411784 litres, so dividing litres by 3.7854 gives US gallons; one UK gallon is 4.54609 litres.
Use inside measurements, and measure the height of the water rather than the glass. The result is the full-tank figure: gravel, rocks, wood and equipment displace water, so the volume you can actually pour in is lower.
Common mistakes
- Measuring the outside of the glass instead of the inside.
- Using the height of the tank instead of the height of the water.
- Treating the full-tank figure as the real water volume when the tank is full of decor.
- Mixing units, for example length in centimetres and height in inches. Choose one unit system.
- Using this rectangular formula for bow-front or hexagonal tanks, whose volume is different.
Good to know
- Dosing products and calculating water changes both depend on volume, so measure carefully.
- If you know how many litres you can fill with a bucket, you can check your calculation by filling the empty tank in measured buckets.
- Use the Aquarium Water Change Calculator once you know your volume.
Frequently asked questions
How do I measure my aquarium?
Measure the inside length, width and the height of the water (not the glass), in centimetres or inches. For a round tank measure the inside diameter.
Is the real water volume smaller?
Yes. Gravel, rocks and decorations displace water, so the volume you can actually pour in is lower than this full-tank figure.
How many litres is a US gallon?
One US gallon is 3.785411784 litres, so divide litres by 3.7854 to get US gallons.
How do I measure a round tank?
Measure the inside diameter and the height of the water. The calculator uses π × radius² × height.
How do I convert litres to gallons?
Divide litres by 3.7854 for US gallons or by 4.546 for UK gallons. The calculator shows both.
Can I use it for bow-front or hexagonal tanks?
Not accurately. Their volume differs from a plain box, so use the maker's stated volume or fill the tank in measured buckets.
Sources
- Pure arithmetic / unit conversion on user inputs (no external constant)
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