About this tool
The Filter Turnover Calculator is a free, in-browser tool that answers two aquarium questions: what filter flow rate you need for a healthy turnover, and whether a filter you already own is actually strong enough once real-world losses are accounted for. Turnover is how many times per hour the entire tank volume passes through the filter. Everything runs locally in your browser.
Required flow = tank volume × target turnover. The target depends on the tank: about 4× for a community or planted tank, 6× for a heavily stocked or semi-aggressive setup, and 8–10× for messy fish like cichlids or goldfish (reef systems aim for 20–40× total flow, but most of that comes from powerheads, not the filter). Enter gallons for a result in GPH or liters for LPH. For the adequacy check, a filter's box rating is optimistic: media, head height and clogging typically cut real throughput roughly in half, so effective flow = rated × 0.5, and actual turnover = effective flow ÷ volume. If that falls below your target, the filter is undersized.
As a worked example, a 55-gallon community tank at a 4× target needs 55 × 4 = 220 GPH. A filter rated at 350 GPH really delivers about 175 GPH after derating, giving an actual turnover of 175 ÷ 55 ≈ 3.2× — below the 4× target, so you would want a stronger filter or a supplementary powerhead. Choosing a filter rated well above the bare minimum (often 1.5–2× the target GPH) leaves headroom as media loads up between cleanings.