How do you calculate filter run time?

Divide pool volume by filter flow rate, then multiply by target daily turnovers. For 20,000 gal, a 3,900 gph filter, and 2 turnovers/day: 20,000 / 3,900 x 2 = 10.26 hours per day.

How many hours a day should a pool filter run?

Enough to hit your turnover target; commonly 8 to 12 hours for residential pools. In the worked example, two daily turnovers require about 10.3 hours of run time.

How do I convert filter flow from gpm to gph?

Multiply gpm by 60. A 65 gpm filter equals 3,900 gph, which is the value to enter in the filter flow rate field.

What is a daily turnover?

One turnover circulates a volume of water equal to the entire pool through the filter once. Many residential pools target 1 to 2 turnovers per day; heavily used or commercial pools require more.

Why is my pool cloudy even though the timer runs long enough?

A fouled filter or partly closed valve reduces actual flow below the rated gph, so fewer real turnovers occur than the schedule assumes. Verify flow with a gauge, then recompute.

Run time vs. turnover time: what is the difference?

Turnover time is how long one full turnover takes; run time is total daily hours across the turnovers you want. Two turnovers of about 5.1 hours each add up to the roughly 10.3-hour daily run time.

Pool, Spa & Water Treatment Chemistry calculator

Pool Filter Run Time Calculator

Filter run time is the number of hours per day a filtration system must operate to achieve a target number of complete water turnovers. Pool operators and service techs use it to set timer schedules that keep water clear and chemically balanced without running the pump around the clock. Run too few hours and the water clouds, chlorine demand climbs, and algae gains a foothold; run too many and energy costs rise for no added clarity. It translates a turnover goal directly into a defensible, on-the-schedule number of hours.

What this calculator does

Estimate filter run time needed from pool volume, filter flow rate, and target turnovers.
Use it to set pump schedules and compare filtration energy tradeoffs.
It computes the daily filter run time in hours needed to circulate a pool's volume a target number of times at a given filter flow rate.

Formula used

Filter run time = pool volume / filter flow rate x target daily turnovers

Inputs explained

Pool water volume: Use calculated or measured pool volume.
Filter flow rate: Multiply flow in gpm by 60 to convert to gallons per hour. For 65 gpm, enter 3900.
Target daily turnovers: Use operating plan or code minimum. Many residential pools target 2 per day.

How to use the result

Use it when programming pump timers, adjusting run time seasonally, or diagnosing water clarity problems tied to insufficient turnover.
It assumes the filter actually delivers its stated flow; a dirty filter or clogged basket drops real flow and quietly extends the true run time needed.

Current U.S. benchmarks

Global copper trades at $13,552 per tonne (IMF via FRED, Jun 2026), up 37.8% in a year, and U.S. industrial electricity averages 8.66 cents per kWh. Both feed electrified-hardware unit economics.

Common questions

How do you calculate filter run time? Divide pool volume by filter flow rate, then multiply by target daily turnovers. For 20,000 gal, a 3,900 gph filter, and 2 turnovers/day: 20,000 / 3,900 x 2 = 10.26 hours per day.
How many hours a day should a pool filter run? Enough to hit your turnover target; commonly 8 to 12 hours for residential pools. In the worked example, two daily turnovers require about 10.3 hours of run time.
How do I convert filter flow from gpm to gph? Multiply gpm by 60. A 65 gpm filter equals 3,900 gph, which is the value to enter in the filter flow rate field.
What is a daily turnover? One turnover circulates a volume of water equal to the entire pool through the filter once. Many residential pools target 1 to 2 turnovers per day; heavily used or commercial pools require more.
Why is my pool cloudy even though the timer runs long enough? A fouled filter or partly closed valve reduces actual flow below the rated gph, so fewer real turnovers occur than the schedule assumes. Verify flow with a gauge, then recompute.

Last reviewed 2026-05-12.