Pool Turnover Rate Calculator
Turnover time
6.7 hours
At 50 GPM, your pump moves the full 20,000 gallons once every 6.7 hours.
- Turnovers per day
- 1.5 (pump running 10 h)
- Water filtered per day
- about 78%
How it's calculated
The last line is the standard dilution model for a well-mixed tank: filtered water mixes with unfiltered water, so each turnover cleans a smaller share of what is left. It explains why pools look best when the pump runs longer, not just faster.
Worked example
A 20,000 gallon pool with a pump moving 50 GPM, running 10 hours a day:
- Turnover time: 20,000 ÷ 50 ÷ 60 = 6.7 hours.
- Turnovers per day: 10 ÷ 6.7 = 1.5.
- Water filtered per day: 1 − e^(−1.5) ≈ 78%.
To hit an 8-hour turnover in the same pool you would need 20,000 ÷ 480 = 42 GPM, which a variable-speed pump can run at a low, quiet speed.
Turnover time by pool size and flow
| Pool | 30 GPM | 40 GPM | 50 GPM | 60 GPM | 80 GPM |
|---|---|---|---|---|---|
| 10,000 gal | 5.6 h | 4.2 h | 3.3 h | 2.8 h | 2.1 h |
| 15,000 gal | 8.3 h | 6.3 h | 5 h | 4.2 h | 3.1 h |
| 20,000 gal | 11.1 h | 8.3 h | 6.7 h | 5.6 h | 4.2 h |
| 30,000 gal | 16.7 h | 12.5 h | 10 h | 8.3 h | 6.3 h |
Share of water filtered
| Turnovers | Filtered |
|---|---|
| 0.5 | 39% |
| 1 | 63% |
| 1.5 | 78% |
| 2 | 86% |
| 3 | 95% |
Frequently asked questions
What is a good turnover rate for a pool?
Most residential pools are designed for one turnover every 6 to 8 hours, and many owners run the pump long enough for one to two turnovers a day. Public pools usually need faster turnovers set by local health codes.
How do I calculate pool turnover?
Divide the pool volume in gallons by the pump flow in gallons per minute, then divide by 60. A 20,000 gallon pool with a 50 GPM pump turns over every 20,000 ÷ 50 ÷ 60 = 6.7 hours.
Does one turnover filter all the water?
No. Filtered water mixes back into the pool, so after one turnover only about 63% of the original water has passed through the filter, and about 86% after two. That is why one turnover a day is a minimum, not a target to beat.
How long should I run my pool pump each day?
At least long enough for one turnover. With a variable-speed pump, run it longer at a low speed: half the speed moves half the water for roughly an eighth of the power, so long slow runs filter more for less money.
How do I know my pump flow rate?
Variable-speed pumps often display GPM. Otherwise read it off the pump curve at your system head (see the pump size calculator), or install an inexpensive flow meter on the return line.
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