PumpCost Atlas

Pool turnover rate calculator

Turnover is how long your pump takes to push one pool's worth of water through the filter. It is a division: gallons ÷ (gallons per minute × 60). Enter a volume and a flow for the hours, or a volume and a target turnover for the flow you need.

1. Pool volume

Know it already? Type it in and skip the helper. Otherwise the helper below fills this field.

Volume helper (pure geometry)

This is geometry, not a survey. A rectangle is length × width × average depth; a circle is π × (diameter ÷ 2)² × average depth. Cubic feet become gallons at 7.48052 US gallons per cubic foot, which is the exact definition of a US gallon as 231 cubic inches. Average depth means the average over the whole surface, so for a pool that slopes it is not the midpoint of the shallow and deep ends unless the slope is uniform across the full length. Freeform, kidney and L-shaped pools are not covered here: measure sections and add them, or get the figure from the builder's plan.

2. Flow, or a turnover target

Flow from a certified record is the flow measured at that test point's head — 8 feet of water at the low-speed point for most in-ground records. Your plumbing almost certainly presents more resistance than that, and more head means less flow at the same rpm. A flow meter on the return line is the honest source; a pressure gauge plus the manufacturer's own pump curve is the next best.

Result

Turnover at this flow
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Turnovers per 24 hours
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Flow needed for the target
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Volume used
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The arithmetic turnover hours = gallons ÷ (gpm × 60)
turnovers per day = 24 ÷ turnover hours
gpm needed = gallons ÷ (target hours × 60)
rectangular gallons = length × width × average depth × 7.48052
round gallons = π × (diameter ÷ 2)² × average depth × 7.48052

What a turnover figure does and does not settle

One turnover does not mean every drop has been filtered. Filtered water mixes back into the pool, so after one turnover a well-mixed pool has had roughly 63% of its water through the filter, and it takes about three turnovers to reach 95%. That is the nature of mixing, not a defect in the pump. It is also why turnover targets are rules of thumb rather than a hygiene guarantee.

How many turnovers a day your pool needs is a local question. Health departments set the requirement for public pools, and the figures vary by jurisdiction and pool type; residential pools are generally not covered by those rules at all. This calculator therefore does not tell you a target — it converts between volume, flow and hours so you can apply whatever requirement or habit you are working to. If you want a defensible number for a public or semi-public pool, the requirement in your state or county's pool code is the only one that counts.

Two practical consequences. First, running longer at a lower speed can deliver the same turnover for far less energy, because power falls much faster than flow when speed drops — that is the whole case for a variable-speed pump, and you can price it in the cost calculator. Second, flow is capped by your plumbing, not only by the pump: pipe diameter, fittings and filter condition set the head the pump works against, and oversizing the pump against narrow pipe buys noise and wear rather than turnover.

Related

Once you know the flow you need, find a certified record that measures near it. The flow figures in the dropdown come straight from each record's test points, and each record has a page: the Hayward TriStar VS measured 25.19 gpm at its low-speed point and 48.44 gpm at its high-speed point, the Pentair IntelliFlo VS and the Jandy VS FloPro publish their own pair, and the full set is grouped by maker on the Hayward, Pentair and Jandy hubs.

Then price the schedule with the pool pump energy cost calculator, which can hold two pumps against the same hours and electricity rate, or read how the weighted energy factor folds flow and power into one number.