Aquarium Volume Calculator
Calculate the volume of your fish tank in litres and US gallons, and get fish stocking estimates based on the inch-per-gallon rule.
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How to use this calculator
For rectangular tanks, multiply length × width × height in centimetres and divide by 1000 to convert to litres. For cylindrical tanks, use the circle area formula (π × radius²) multiplied by height. The result is reduced by the fill percentage and used with the stocking rules.
- 1
Select your tank shape (rectangular, cylindrical, or bow-front).
- 2
Enter the tank dimensions in centimetres.
- 3
Enter how full you fill the tank (typically 80–90%).
- 4
Read the water volume and stocking capacity estimates.
Frequently asked questions
What is the inch-per-gallon rule?
The basic rule is 1 inch (2.5cm) of adult fish body length per 1 US gallon (4.5L) of water. This is a conservative guideline for small community fish. Large, messy, or aggressive fish need more space per fish.
How do I convert litres to US gallons?
1 US gallon = 3.785 litres. So divide litres by 3.785, or multiply by 0.264. A common 60×30×36cm tank holds approximately 58L or about 15 US gallons (after accounting for 90% fill).
Does tank size affect filtration needs?
Yes — a general guideline is to use a filter rated for at least 5–10× the tank volume per hour (turnover rate). For a 60L tank, use a filter rated for 300–600 L/hour.
Aquarium Volume Calculator — Fish Tank Litres, Gallons, and Stocking
How to Measure Your Fish Tank Volume
For rectangular tanks: multiply length × width × height in centimetres, then divide by 1,000 to get litres. Fill level matters — most tanks are filled to 80–90% of total capacity to allow for substrate, decorations, and surface agitation.
Fish Stocking Rules Explained
The classic 1 inch per gallon rule (2.5cm per 4.5L) is a starting guide for small community fish under 5cm. For larger fish, bottom-dwellers, or species with high bioload (goldfish, cichlids), you need significantly more water volume per fish.
Popular Tank Sizes in Litres and Gallons
Common tank sizes: 20L nano (5 gal), 40L starter (10 gal), 75L community (20 gal), 115L standard (30 gal), 200L display (53 gal). Larger tanks are generally easier to maintain as the greater water volume buffers against parameter fluctuations.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →