Turnover and run-time calculator
Two numbers decide a pool’s run time: how fast the water moves and how much filter it has to move through. This gives you both, and flags the filter that is being driven past the point of catching anything.
Turnover is how long the pump needs to push a pool's worth of water through the filter once. Two turnovers a day is the working habit on a residential pool.
One turnover
7.3hours
- Run time for two turnovers
- 14.7 h/day
- Filtration rate
- 1 gpm/ft²
- Filter loading
- within the maker rating
A sand filter driven above about 15–20 gpm per square foot of media passes dirt straight through, whatever the pressure gauge says; DE and cartridge filters are rated far lower (about 2 and 1 gpm per square foot on Hayward's published ratings), and the verdict above checks the type you picked. If your rate is high, the answer is more filter area or a slower pump speed, not a longer run.
Turnover is a filter question
Turnover asks how long the pump needs to send one pool’s worth of water through the filter. It is not a promise that every molecule has been filtered — mixing means a single turnover treats roughly two-thirds of the water — which is why two turnovers a day is the working habit rather than one.
How to use it
- Enter the pool volume in gallons — the pool volume calculator gives it from the dimensions.
- Enter the flow through the filter in gallons per minute, from a flow meter or the pump curve at your head — not the figure on the pump label.
- Enter the filter media area in square feet from the filter’s own label. A 24-inch sand filter is about 3.1 ft²; cartridges carry far more, which the filter comparison sets side by side.
- Pick the filter type. Sand, DE and cartridge are rated very differently (about 20, 2 and 1 gpm per square foot on Hayward’s published ratings), so the verdict checks yours.
- Read the hours for one turnover, the daily run for two, and the filtration rate with its verdict.
Worked example
A 15,000 gallon pool on a 24-inch sand filter (3.1 ft² of media), first at 50 gpm and then with the pump slowed to 35 gpm:
| Step | Working | Result |
|---|---|---|
| One turnover at 50 gpm | 15,000 ÷ 50 ÷ 60 | 5 h |
| Two turnovers | 5 × 2 | 10 h/day |
| Filtration rate | 50 ÷ 3.1 ft² | 16.1 gpm/ft², top of range |
| One turnover at 35 gpm | 15,000 ÷ 35 ÷ 60 | 7.1 h |
| Two turnovers | 7.1 × 2 | 14.3 h/day |
| Filtration rate | 35 ÷ 3.1 ft² | 11.3 gpm/ft², within the rating |
The slower speed costs more hours a day but brings the filter back into range — the trade the next section explains.
The number nobody checks
Filtration rate — gallons per minute per square foot of media — decides whether the filter is actually catching anything. Push water through too fast and fine debris goes straight past the sand while the pressure gauge sits reassuringly normal. That is the most common cause of a pool that is clean on paper and cloudy in daylight.
| Rate (sand filter) | Reading | What to do |
|---|---|---|
| Under 15 gpm/ft² | In range | Nothing |
| 15–20 gpm/ft² | Top of range | Drop pump speed if you can |
| Over 20 gpm/ft² | Over-driven | More filter area, or slower — not a longer run |
Measure the flow, do not read the plate
The gallons per minute on a pump label is what it does at zero head. Real flow comes off a flow meter, or from the pump curve at your measured head — the pump sizing tool estimates the head for you.
What a longer run does and does not fix
Running longer fixes an under-filtered pool. It does not fix an over-driven filter, a channelled sand bed or a torn cartridge, and it certainly does not fix chemistry. If two turnovers a day still leave the water dull, take the filter apart — start with cleaning it properly.