Pool Pump Size Calculator
Choose a circulation calculation
Find required filtered flow or check the turnover produced by an actual flow rate.
Calculate the circulation flow needed to move one pool volume through the filtration path in the turnover time you choose, or check the turnover time produced by an actual measured or pump-curve flow. Use US gallons and gallons per minute, or cubic metres and m³/h. The result is a circulation-flow target, not a pump horsepower recommendation. Selecting equipment also requires total dynamic head, the pump curve, filter and heater limits, pipework, fittings and locally applicable pool rules.
How to calculate pool circulation flow
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1
Choose size or check mode
Find the flow required for a user-supplied turnover time, or calculate turnover from the actual flow through the filtration system.
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2
Enter volume and time or flow
Use gallons and hours with a GPM result, or cubic metres and hours with an m³/h result. Use the full circulating pool volume.
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3
Verify the equipment path
Compare the result with the pump curve at the system’s total dynamic head and with filter, heater, plumbing and local-rule limits.
Pool volume, circulation flow and turnover
Turnover time is the theoretical time required for a volume equal to the pool’s total volume to pass through the filtration process. The CDC Model Aquatic Health Code defines calculated turnover from total water volume divided by filtration flow, and excludes water moved by a separate feature pump when that water does not pass through filtration. The CDC also explains that the MAHC is guidance rather than federal law and only has legal effect where a jurisdiction adopts it.
For preliminary circulation math:
required GPM = pool volume in US gallons ÷ (turnover hours × 60)
required m³/h = pool volume in m³ ÷ turnover hours
To check an actual operating flow, reverse the formula:
turnover hours = pool volume in gallons ÷ (actual GPM × 60)
or turnover hours = pool volume in m³ ÷ actual m³/h.
| What you know | Imperial calculation | Metric calculation |
|---|---|---|
| Volume and chosen turnover | GPM = gallons ÷ (hours × 60) |
m³/h = m³ ÷ hours |
| Volume and actual flow | hours = gallons ÷ (GPM × 60) |
hours = m³ ÷ (m³/h) |
| One full theoretical turnover | A volume equal to the entered gallons | A volume equal to the entered m³ |
Worked examples
For a 20,000 US gallon pool and a user-chosen 8-hour turnover, the preliminary flow is 20,000 ÷ (8 × 60) = 41.67 GPM. That number is the flow the circulation path must actually deliver; it is not a motor or nameplate selection.
In metric units, a 75 m³ pool with a chosen 6-hour turnover needs 75 ÷ 6 = 12.50 m³/h. If a flow meter instead shows 10 m³/h, the calculated turnover is 75 ÷ 10 = 7.50 hours.
Why flow does not determine horsepower
A pump produces different flow at different total dynamic head (TDH). Pipe diameter and length, elevation, fittings, valves, drains, skimmers, a dirty filter, heater and other equipment all affect the operating point. The current CDC MAHC materials state that recirculation pumps should meet design flow at the maximum TDH required by the entire system, including demanding conditions such as a filter needing backwash. The filter, heater, chlorinator and plumbing may also impose minimum or maximum flow limits.
This calculator therefore does not recommend horsepower, pipe size, pump speed, filter size or a legally required turnover time. Public-pool rules vary by venue type and jurisdiction, while residential requirements and manufacturer instructions differ again. Confirm the chosen turnover target, suction-safety provisions, equipment ratings, hydraulic design and local approvals with the authority having jurisdiction, equipment manufacturers and a qualified pool professional.
Frequently Asked Questions
No. Horsepower cannot be selected from flow alone. Use the required flow together with a calculated total dynamic head and the manufacturer’s pump curve, then check the complete equipment and plumbing path.
Enter the turnover time required by your adopted local rules, facility design or qualified pool professional. Requirements can differ for residential pools, public pools, spas, wading pools and aquatic features, so the calculator does not choose a value for you.
The calculator uses Livewire, so selected values are sent to this site to update results. Funnel mode may also place non-sensitive values in the page URL. Do not enter confidential project information.
No. The result is only volume-and-time circulation math. Compliance and workable operation also depend on actual flow at TDH, pump and equipment listings, filter and heater limits, plumbing, suction safety, water treatment and locally adopted requirements.
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