Aquarium Calculator
Estimate aquarium water volume from inside dimensions and user-selected fill and water-change percentages.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
Use internal dimensions in inches. Rectangle, cylinder and right-triangle corner shapes use their geometric footprints.
Worked example
calculated with the default values below
Internal length / cylinder diameter 36 in · Maximum internal front-to-back depth 18 in · Tank height 20 in · Substrate depth 2 in · Fill level 95 % · Chosen water-change percentage 25 % · Tank shape Rectangular · Fill flow (US gal/min) 5 · Front bow depth (in) 3 · Primary result Estimated water volume Estimated water volume 48.0 gal · Nominal volume 56.1 gal · Estimated water volume 181.6 L · Weight of the water 400 lb · Water for the chosen change 12.0 gal · Time to fill with a 5 gal/min tap 9.6 min · Volume 12,960 cu in
Method and assumptions
Use internal dimensions in inches. Rectangle, cylinder and right-triangle corner shapes use their geometric footprints. Bow-front uses a straight rectangle plus a circular segment defined by the entered bow depth; cylinder length means diameter. Nominal volume differs from water volume: subtract a solid substrate depth, then apply fill percent to the remaining height. US gallons are 231 in³; water weight is an approximate 8.34 lb/gal, excluding tank and equipment. Width is the maximum internal front-to-back depth. Bow depth is subtracted to obtain the rectangular depth before the circular segment is added; it must not exceed the total width or half the length. Only a minor circular-segment front is modeled.
General background references
Disclaimer
These calculators offer general guidance and do not replace veterinary advice. Individual animals vary with breed, weight, health status and medication. Suspected poisoning from chocolate, medication, plants or chemicals is an emergency — contact your veterinarian or a pet poison control service immediately rather than relying on a calculator.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
nominal US gal = footprint_in² × height_in/231; water US gal = footprint × (height − substrate) × fill%/100/231; L = US gal × 3.785411784
Bow depth is subtracted to obtain the rectangular depth before the circular segment is added; it must not exceed the total width or half the length. Only a minor circular-segment front is modeled.
Frequently asked questions
Why can the estimated water volume differ from the tank label?
Use internal dimensions in inches. Rectangle, cylinder and right-triangle corner shapes use their geometric footprints. Bow-front uses a straight rectangle plus a circular segment defined by the entered bow depth; cylinder length means diameter. Nominal volume differs from water volume: subtract a solid substrate depth, then apply fill percent to the remaining height. US gallons are 231 in³; water weight is an approximate 8.34 lb/gal, excluding tank and equipment. Width is the maximum internal front-to-back depth. Bow depth is subtracted to obtain the rectangular depth before the circular segment is added; it must not exceed the total width or half the length. Only a minor circular-segment front is modeled.