# What pool pump flow do I need?

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.

- Page: https://www.acalculator.org/construction/pool-pump-calculator
- JSON spec: https://www.acalculator.org/construction/pool-pump-calculator.json
- Version: c841be7d8853

## Default answer

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).

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| by | I know | The pool volume, or the pool’s size to work the volume out from. |
| v | Pool volume | How much water the pool holds. |
| vu | Volume unit | US gallons, liters or cubic meters. |
| shape | Shape | A rectangular pool, or a round one. |
| lu | Size in | Feet or meters for the pool size. |
| l | Length | The length of a rectangular pool. |
| w | Width | The width of a rectangular pool. |
| dia | Diameter | The inside diameter of a round pool. |
| d | Average depth | The average water depth: (shallow end + deep end) ÷ 2 for a sloped floor. |
| h | Turnover time (hours) | The time the pump should take to move the whole pool volume through the filter once. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| gpm | Flow rate (gal/min) | Volume in US gallons ÷ minutes of turnover. |
| lpm | Flow rate (L/min) | Volume in liters ÷ minutes of turnover. |
| m3h | Flow rate (m³/h) | Volume in cubic meters ÷ hours of turnover. |
| gallons | Pool volume (US gal) | The pool volume in US gallons. |
| liters | Pool volume (L) | The pool volume in liters. |

## Method

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

## Assumptions

- 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.

## Worked examples

1. by = volume, v = 20,000, vu = gal, h = 8 gives gpm = 41.7, lpm = 157.7, m3h = 9.46, liters = 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. by = size, shape = rect, lu = ft, l = 32, w = 16, d = 5, h = 6 gives gallons = 19,150, gpm = 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. by = size, shape = round, lu = m, dia = 5, d = 1.2, h = 8 gives m3h = 2.95, lpm = 49.1.
4. by = volume, v = 50, vu = m3, h = 0.5 gives m3h = 100, lpm = 1,666.7.

## FAQ

### 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.

## Sources

- CDC, Model Aquatic Health Code (turnover times for public aquatic venues). https://www.cdc.gov/model-aquatic-health-code/php/our-work/index.html (retrieved 2026-10-19)
- NIST Handbook 44 (2024), Appendix C, General Tables of Units of Measurement (1 US gallon = 231 cubic inches). https://www.nist.gov/document/nist-hb-44-2024-appendix-c-general-tables-units-measurement (retrieved 2026-10-19)
- NIST Special Publication 811 (2008), Appendix B.8: 1 in = 0.0254 m and 1 ft = 0.3048 m exactly. https://www.nist.gov/pml/special-publication-811 (retrieved 2026-10-19)