Pool owners size pumps the way they size everything else: bigger feels safer. In pool circulation, oversized is a real problem, and the sizing number is not the pump's maximum flow but the pool's turnover rate.
Turnover is the whole calculation
The water in the pool must pass through the filter a set number of times a day. A residential pool typically targets a full turnover every 6 to 8 hours; a busy commercial pool may want 4 hours or less. Divide the pool volume by the turnover window and you have the required flow: a 60 m³ pool on an 8-hour cycle needs a pump delivering 7.5 m³/h, not the biggest unit in the catalogue.
Why oversizing backfires
- Filtration worsens. Sand filters have an optimal velocity; push water through too fast and particles pass straight through. A bigger pump can make the water dirtier.
- Energy multiplies. Pump power scales with the cube of speed. A pump a third too large costs roughly twice the electricity to do a worse job.
- Components wear. Excess velocity stresses laterals, seals and pipework for no benefit.
The quiet trend in pool duty is variable-speed circulation: run longer at lower speed, and the pool stays clearer on a fraction of the energy. Sized to the turnover, not to the badge, is the rule that matters.