Does the calculator account for gravel and decorations?

No — it calculates the full geometric volume of the tank. In practice, substrate, rocks, and decorations displace roughly 10–20% of the total volume. A common rule of thumb is to multiply the result by 0.85 for a realistic water volume estimate.

What is the fish-per-gallon rule?

The classic guideline is 1 inch of adult fish body length per gallon of water. This is a rough starting point only — waste load, filtration capacity, and species behavior matter more for long-term health.

How do I measure a bowfront tank?

Measure the straight-line width (front edge to back panel), the outside length (end to end), and the height. The calculator uses these to estimate the additional volume from the curved front bow.

Why are US gallons different from Imperial gallons?

A US gallon is 231 cubic inches (3.785 L), while an Imperial gallon is 277.4 cubic inches (4.546 L). Most North American fish-keeping resources use US gallons; UK and Australian resources use Imperial or liters.

Can I use centimeters instead of inches?

Yes — toggle the unit selector to cm before entering dimensions. The calculator handles the conversion internally.

Aquarium Volume Calculator

Name: Aquarium Volume Calculator
Availability: InStock
Author: Nham Vu

Enter your tank dimensions to instantly calculate water volume in gallons and liters for rectangular, cylindrical, or bowfront aquariums.

Tank Dimensions

Tank Shape

Dimension Unit

Length

Width

Height

Enter dimensions and click Calculate Volume.

Summary

Enter your tank dimensions to instantly calculate water volume in gallons and liters for rectangular, cylindrical, or bowfront aquariums.

How it works

Select your tank shape: rectangular, cylindrical, or bowfront.
Enter the dimensions (length, width, height, or diameter) in inches or centimeters.
The calculator applies the correct volume formula for your tank shape.
Results display instantly in US gallons, Imperial gallons, and liters.
Use the stocking guide to estimate the maximum number of small fish for your tank.

Use cases

Determine how many fish you can safely stock in a new aquarium.
Calculate the correct dose of water conditioners and medications.
Compare tank sizes when shopping for a new aquarium.
Estimate how long it will take to fill a tank with a known flow rate.
Convert between gallon and liter measurements for international fish-keeping resources.
Plan the water change volume needed for weekly maintenance.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu