About

This is a free aquarium volume and stocking calculator that runs entirely in your browser. Enter the inside dimensions of a rectangular tank and it returns the nominal capacity in both gallons and litres, the actual water volume once substrate and headspace are removed, and a stocking range derived from the classic one-inch-per-gallon guideline applied to that corrected volume.

Everything is computed locally in JavaScript using the exact conversion constants — 231 cubic inches per US gallon and 1,000 cubic centimetres per litre, with 3.785411784 litres per gallon for converting between the two. Nothing you type is sent to a server, there is no sign-up, and there are no third-party scripts or frameworks. Displayed values are truncated to two decimal places rather than rounded up, so the tool never reports more water than your measurements support.

It is not fishkeeping advice and it is not a substitute for researching the species you intend to keep. Real stocking capacity depends on filtration, planting, water change routine, and the temperament and adult size of individual species — none of which a calculator can know. Check the requirements of every species before you buy one, and when the numbers and an experienced fishkeeper disagree, believe the fishkeeper.