acalculator

What pool pump flow do I need?

Type your pool volume, or its size and average depth, and how many hours a full turnover should take. The pool pump calculator gives the flow rate the pump and filter must move.

Your numbers

I know
Flow rate (gal/min)
41.7

The pump needs about 41.7 gallons per minute (9.46 m³/h).

Flow rate (L/min)
157.7
Flow rate (m³/h)
9.46
Pool volume (US gal)
20,000
Pool volume (L)
75,708

Flow rate (gal/min): 41.7. The pump needs about 41.7 gallons per minute (9.46 m³/h).

How to calculate

Works out the pump flow rate a pool needs to turn its whole volume over in a chosen time, in gallons per minute, liters per minute and cubic meters per hour, from the volume or the pool’s size.

Example with the default inputs (I know Volume, Pool volume 20,000, Volume unit US gallons, Turnover time (hours) 8): The pump needs about 41.7 gallons per minute (9.46 m³/h).

Method: flow = pool volume ÷ turnover time. Rectangle volume = length × width × average depth; round = π × (diameter ÷ 2)² × depth.

  • The flow is the rate that moves the whole pool volume once in the turnover time; the pump must deliver it against the head loss of your pipes and filter.
  • Your local health code sets the turnover time for a public pool; for a home pool, choose a time to suit how the pool is used.
  • 1 US gallon = 231 cubic inches = 3.785411784 L; 1 ft = 0.3048 m.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. I know Volume, Pool volume 20,000, Volume unit US gallons, Turnover time (hours) 8 gives Flow rate (gal/min) 41.7, Flow rate (L/min) 157.7, Flow rate (m³/h) 9.46, Pool volume (L) 75,708.Source: NIST Handbook 44 (2024), Appendix C (1 gal = 231 in³), https://www.nist.gov/document/nist-hb-44-2024-appendix-c-general-tables-units-measurement; NIST SP 811, Appendix B.8 (1 in = 0.0254 m, 1 ft = 0.3048 m), https://www.nist.gov/pml/special-publication-811
  2. I know Pool size, Shape Rectangle, Size in feet, Length 32, Width 16, Average depth 5, Turnover time (hours) 6 gives Pool volume (US gal) 19,150, Flow rate (gal/min) 53.2.Source: NIST Handbook 44 (2024), Appendix C (1 gal = 231 in³), https://www.nist.gov/document/nist-hb-44-2024-appendix-c-general-tables-units-measurement; NIST SP 811, Appendix B.8 (1 in = 0.0254 m, 1 ft = 0.3048 m), https://www.nist.gov/pml/special-publication-811
  3. I know Pool size, Shape Round, Size in meters, Diameter 5, Average depth 1.2, Turnover time (hours) 8 gives Flow rate (m³/h) 2.95, Flow rate (L/min) 49.1.
  4. I know Volume, Pool volume 50, Volume unit cubic meters, Turnover time (hours) 0.5 gives Flow rate (m³/h) 100, Flow rate (L/min) 1,666.7.

How it works

flow rate = pool volume ÷ turnover time

Pool volume V in cubic meters:

  • Typed: US gallons × 0.003785411784 (1 gal = 231 in³ and 1 in = 0.0254 m, exactly), liters ÷ 1,000, or cubic meters.
  • Rectangle: length × width × average depth.
  • Round: π × (diameter ÷ 2)² × average depth.
  • Sizes in feet are converted with 1 ft = 0.3048 m exactly.

Results, with T the turnover time in hours:

  • gal/min = (V ÷ 0.003785411784) ÷ (T × 60)
  • L/min = V × 1,000 ÷ (T × 60)
  • m³/h = V ÷ T
  • Pool volume in US gallons and in liters.

Inputs and limits

  • Volume: 1 to 100,000,000 in the unit chosen. Length, width, diameter and average depth: 0.1 to 1,000 ft or m. Turnover time: 0.1 to 48 hours.
  • Typed values are read as exact decimals and every step is exact, except π for a round pool. Shown values are rounded half up: gal/min and L/min to 1 decimal, m³/h to 2 decimals, volumes to whole gallons and liters.

Worked examples by hand

20,000 gallons in 8 hours: 20,000 ÷ 480 min = 41.7 gal/min. 20,000 gal = 75,708.24 L, so 75,708.24 ÷ 480 = 157.7 L/min and 75.70824 m³ ÷ 8 = 9.46 m³/h.

32 × 16 ft rectangle, 5 ft average depth, 6 hours: 32 × 16 × 5 = 2,560 ft³; × 1,728 ÷ 231 = 19,150 gal. 19,150.13 ÷ 360 = 53.2 gal/min.

Round pool 5 m across, 1.2 m deep, 8 hours: π × 2.5² × 1.2 = 23.56 m³. 23.56 ÷ 8 = 2.95 m³/h = 49.1 L/min.

50 m³ in 30 minutes: 50 ÷ 0.5 = 100 m³/h = 1,666.7 L/min.

Other questions people ask

How do I work out the flow rate a pool pump needs?

Divide the pool volume by the turnover time in minutes. A 20,000 gallon pool turned over in 8 hours needs 20,000 ÷ (8 × 60) = 41.7 gallons per minute.

What is pool turnover time?

The time the pump takes to move a volume of water equal to the whole pool through the filter once. A shorter turnover filters the water more often but needs more flow. Public pools must meet the turnover time in their local health code, which the CDC Model Aquatic Health Code helps set.

How do I find my pool volume?

Multiply length × width × average depth for a rectangle, or π × (diameter ÷ 2)² × average depth for a round pool. One cubic foot holds 7.48 US gallons (1,728 ÷ 231). The average depth of a sloped pool is (shallow end + deep end) ÷ 2.

Is the flow rate the same as the pump size?

No. The flow rate is what the pump must deliver. A pump’s actual flow drops as the pipes, fittings and filter add resistance (head), so check the pump’s flow curve at your system’s head, and make sure the filter is rated for the flow.

Can the flow be too high?

Yes. Every filter has a maximum flow rate, and a pump that pushes past it filters poorly and wears the filter. Choose a turnover time that keeps the flow within the filter’s rating.