Filter sizing is usually expressed as turnover: how many times per hour the tank volume passes through the filter. The rated flow on the box is measured with no media in the basket and no plumbing resistance, so the flow you actually get in the tank is lower. Enter the water volume, your target turnover and a loss share, and this tool gives both the real flow you need and the rated flow to shop for.
The math is real flow = water volume x turnover and rated = real flow / (1 - loss), with the formula used printed below the results. Neither turnover nor loss has an officially published table. Both move a long way with filter type, media choice and hose length, so this tool supplies no figures and asks for the ones in your own reference (as of October 2026).
This tool does not calculate water change volume, and it does not recommend media or products. More flow does not translate into proportionally better filtration, and a strong current is a burden on species that are weak swimmers. This tool is for reference only and does not replace veterinary care. Contact your veterinarian or an aquatic animal hospital right away if your fish hide from the current or their fins fray.
Frequently Asked Questions
There is no officially recommended table. Enter the figure from your own reference or your fish store. This tool only converts it into a flow rate.
Enter 0 and the rated flow matches the real flow. Densely packed media and long hoses push the loss higher.
No. Flow rate and change volume are separate, and this tool does not calculate change volume. For that you multiply tank volume by a change share.