The formulas we use, no black boxes
Required flow rate (m³/h) = Volume (m³) ÷ Recirculation time (h). As a common industry reference, a community pool turns over all its water in about 4 hours and a private pool in about 6. It isn't a legal figure: RD 742/2013 and Decreto 99/2024 (art. 11.3) require the recirculation time to match the equipment specifications and what the pool needs to meet the quality parameters.
Filter diameter: calculated from a standard filtration speed of 45 m³ per m² of filtering surface, the higher the flow rate, the larger that surface needs to be, so as not to overwork the filter or lose filtering quality.