Free aquarium calculators
Fish tank math, made easy.
Find out how much water your tank really holds, what it weighs set up, and what it needs. Every number is worked out from manufacturers' published specs, with the method shown.
Calculators
- Tank volumeRectangle, bow-front, cylinder, hexagon and corner tanks, in gallons and litres
- StockingHow many fish, with a tank-mate check. Coming soon
- SubstrateSand and gravel in pounds and bags. Coming soon
- Heater sizeWatts for your tank and room. Coming soon
Tank size guides
Exact dimensions from Aqueon and Marineland, real water volume, weight and the stand each tank shares.
- 10 gallon20 × 10 × 12 in
- 20 gallon long30 × 12 × 12 in
- 29 gallon30 × 12 × 18 in
- 40 gallon breeder36 × 18 × 16 in
- 55 gallon48 × 13 × 21 in
- 75 gallon48 × 18 × 21 in
Why these numbers are different
Real water, not the label. A “75 gallon” holds about 65 gallons once it has glass, sand and a gap at the top. Dosing and stocking should use the real figure, so every page shows it.
Sourced, not guessed. Size pages compare the makers' own specs and link to them. Where brands disagree, we show both and explain why.
Free, no sign-up. Every result has a link you can share or embed.