Aquarium Volume Calculator
Gallons in a rectangular fish tank.
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ⓘ Live results
Results
- Total volume
- 50.5 gal
- Recommended fill volume (90%)
- 45.4 gal
- Weight when full (approx)
- 421 lb
Quick answer
Aquarium volume in gallons is length times width times height in inches, divided by 231.
gallons = (length x width x height in inches) / 231
How to use the Aquarium Volume Calculator
- 1Measure the tank's interior length, width and height in inches.
- 2The calculator uses the standard conversion of 231 cubic inches per US gallon.
- 3Use the 90% fill estimate to leave room at the top and avoid overflow with decor and substrate.
Worked example
Using the values the calculator loads with:
Inputs
- Tank length36 in
- Tank width18 in
- Tank height18 in
Results
- Total volume50.5 gal
- Recommended fill volume (90%)45.4 gal
- Weight when full (approx)421 lb
Frequently asked questions
Why not fill the tank 100%?
Leaving headspace prevents overflow when adding substrate, decorations or during water changes.
How much does a full tank weigh?
Water weighs about 8.34 lb per gallon, plus the tank, stand, substrate and decor weight on top of that.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.