Aquarium Volume Calculator
Calculate the water volume of your aquarium in litres, US gallons, and UK gallons. Supports rectangular, cylindrical, and hexagonal tank shapes.
Knowing your tank volume is essential for dosing medications, calculating stocking levels, sizing equipment, and planning water changes. Most aquarium products require an accurate volume to work correctly - guessing can lead to under-dosing or overdosing, both of which stress fish.
Enter your tank dimensions below and the calculator will give you the volume in all three common units used in fishkeeping. If your tank is not a standard rectangle, select the cylinder or hexagonal shape for a more accurate result.
Common tank sizes
- 60 x 30 x 30 cm - 54 litres / 14 US gal
- 80 x 35 x 40 cm - 112 litres / 30 US gal
- 100 x 40 x 50 cm - 200 litres / 53 US gal
- 120 x 40 x 50 cm - 240 litres / 63 US gal
- 150 x 50 x 60 cm - 450 litres / 119 US gal
Calculator
Select your tank shape, choose your measurement unit, and enter the dimensions below.
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Fill in the form and click calculate to see your results here.
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How Tank Volume Is Calculated
Each tank shape uses a different geometric formula. All calculations are done in centimetres (inches are converted first) and the result in cubic centimetres is divided by 1,000 to get litres.
Rectangular tank
Volume = L x W x H / 1,000
Length times width times height in centimetres, divided by 1,000 to convert to litres.
Cylindrical tank
Volume = pi x (D/2)² x H / 1,000
Pi times the radius squared times the height. The radius is half of the diameter.
Hexagonal tank (regular)
Volume = (3 x sqrt(3) / 2) x S² x H / 1,000
The area of a regular hexagon is (3 x sqrt(3) / 2) times the side length squared. Multiply by height and divide by 1,000.
Unit conversions
If you enter measurements in inches, each value is multiplied by 2.54 to convert to centimetres before the volume formula is applied. The resulting litres are then converted: 1 litre = 0.264172 US gallons and 1 litre = 0.219969 UK (imperial) gallons.
Example Calculation
Scenario
You have a standard rectangular aquarium that measures 100 cm long, 40 cm wide, and 50 cm tall.
Volume = 100 x 40 x 50
Volume = 200,000 cm³
Volume = 200 litres
200 litres x 0.264172 = 52.8 US gallons
200 litres x 0.219969 = 44.0 UK gallons
Tip: With substrate and decorations, the actual water volume in this tank would be closer to 170-180 litres. Use the total volume for equipment sizing, but consider the reduced volume when dosing sensitive medications.
Total volume vs actual water volume
The calculator gives you the total geometric volume of the tank. Substrate, rocks, driftwood, internal filters, and heaters all displace water. A heavily aquascaped tank might hold only 80-85% of its total volume in water. For general equipment sizing, use the total. For precise medication dosing, measure how many litres you actually add when filling the tank.
How to measure your tank
Measure the inside dimensions of the glass, not the outside. Glass thickness (typically 4-12 mm depending on tank size) reduces the internal space. For height, measure from the inside base to the water line, not the top rim of the tank.
Frequently Asked Questions
Common questions about aquarium volume and tank sizing.
Why do I need to know my aquarium volume?
Tank volume is the starting point for almost every aquarium calculation. You need it to dose medications and fertilisers correctly, calculate stocking levels, size filters and heaters, and determine water change volumes. An inaccurate volume means inaccurate dosing, which can harm fish.
What is the difference between US gallons and UK gallons?
A US gallon is 3.785 litres, while a UK (imperial) gallon is 4.546 litres - about 20% larger. Most aquarium products sold in the United States use US gallons. If you are in the UK, double-check whether equipment ratings refer to imperial or US gallons, as the difference matters for dosing and filtration.
Should I calculate total volume or actual water volume?
This calculator gives you the total geometric volume of the tank. Your actual water volume will be lower because substrate, rocks, driftwood, and equipment take up space. A common rule of thumb is to estimate usable water at 85-90% of total volume. For precise dosing, measure the water you add when filling the tank from empty.
How do I measure a hexagonal aquarium?
A regular hexagonal tank has six equal sides. Measure the length of one flat side panel (not corner to corner) - that is the side length. Then measure the interior height from the bottom glass to the waterline. Enter both values into the calculator with the hexagonal shape selected.
Can I use this calculator for bow-front or irregular tanks?
This calculator covers the three most common geometric shapes: rectangular, cylindrical, and hexagonal. For bow-front or irregular tanks, you can approximate by using the rectangular calculator with the average depth, or measure your actual water volume by tracking how many litres you add when filling the tank.
Does tank volume affect how many fish I can keep?
Yes. Tank volume is one of the main factors in stocking decisions. More water means more dilution of waste, more stable water parameters, and more swimming space. However, volume alone does not determine stocking - filtration capacity, species temperament, and tank dimensions (length and width matter for territorial fish) are also important.
Related Guides
Learn more about tank setup, equipment sizing, and water management for your aquarium.
Tank Setup Guide
A step-by-step walkthrough of setting up your first aquarium, including equipment placement and cycling.
Read the guideWater Changes
How often to change water, how much to replace, and the right way to do it without stressing your fish.
Read the guideWater Temperature Guide
Why stable temperature matters, how to monitor it, and what happens when it fluctuates too much.
Read the guide