Quick answer: Choose a pool pump by flow rate, not horsepower. Multiply length, width and average depth in metres by 1,000 for litres, divide by your turnover time in hours (usually 8), then by 60. That is the litres per minute needed at your system's head: about 83 for a 40,000 litre pool.
Most pool pump problems come back to size. A pump that is too small cannot turn the whole pool over in the hours it runs, so the filter falls behind and the water turns cloudy. A pump that is too big costs more to run, pushes water through the filter faster than it can clean it and wears its seals out early. This guide gives you a size chart, the method behind it and the figure most people miss, which is head. If you would rather skip the maths, use the free pool pump calculator on our swimming pool pumps page.
Pool pump size chart (litres and flow rate)
Find the pool closest to yours. The flow figures are what the pump must deliver at your system's working head, not the maximum printed on the box.
| Pool | Size (length × width × average depth) | Volume | 6 hour turnover (commercial) | 8 hour turnover (standard) | 12 hour turnover (economy) |
|---|---|---|---|---|---|
| Small above-ground | 4.5 × 2.5 × 1.0 m | 11,250 litres | 31 L/min | 23 L/min | 16 L/min |
| Small in-ground | 6 × 3 × 1.2 m | 21,600 litres | 60 L/min | 45 L/min | 30 L/min |
| Typical domestic | 8 × 4 × 1.3 m | 41,600 litres | 116 L/min | 87 L/min | 58 L/min |
| Large domestic | 10 × 5 × 1.4 m | 70,000 litres | 194 L/min | 146 L/min | 97 L/min |
| Very large domestic | 12 × 6 × 1.5 m | 108,000 litres | 300 L/min | 225 L/min | 150 L/min |
| Large pool (worked example below) | 20 × 8 × 1.0 m | 160,000 litres | 444 L/min | 333 L/min | 222 L/min |
These match the three turnover settings in our calculator. Use 8 hours for most domestic pools and 6 hours for commercial pools or where bather loads are high. Round pools: use π × radius² × depth. A 5 m diameter pool 1.2 m deep holds about 23,560 litres and needs about 49 litres per minute over 8 hours.
How to work it out in four steps
1. Calculate the volume of your pool
Multiply length × width × depth in metres to get cubic metres. If the depth varies, use the average: (shallow end + deep end) ÷ 2. For a round pool, use π × radius² × depth.
2. Convert to litres
One cubic metre is 1,000 litres, so multiply by 1,000.
3. Divide by your turnover time
Turnover is how long it takes for the whole pool to pass through the filter once. The standard for a domestic pool is 8 hours, or 6 hours for commercial pools and where bather loads are high. Our calculator also offers a 12 hour economy setting. Many home owners do not run the pump all day, only for a few hours, so the real question is whether the pump turns the pool over within the hours you actually run it. If you plan to run it for 6 hours a day, size it for a 6 hour turnover. Bear in mind that a faster turnover needs a bigger pump, which costs more to run.
4. Convert to litres per minute
Divide the litres per hour by 60. Every pool pump on our site lists its flow in litres per minute, so you can compare like with like.
Worked example: a pool 20 m long, 8 m wide and 1 m deep holds 20 × 8 × 1 = 160 m³, which is 160,000 litres. Over an 8 hour turnover that is 20,000 litres per hour, or about 333 litres per minute.
Do not forget head
Head is the resistance the pump has to push against. As a working guide, 10 metres of head is roughly 1 bar. The maximum flow printed on a pump is measured at zero head, but a real pool system always has resistance, so the pump delivers less once it is plumbed in. Head comes from:
- suction lift, the height from the pool water up to the pump, and the height back to the return inlets
- friction in the pipework, bends and valves, which rises with longer runs and smaller pipes
- the filter, plus any heat pump, salt cell or other equipment in the circuit
Typical figures for a domestic pool are 0.5–2 m of suction lift, 2–4 m through a clean sand filter (rising as the filter loads between backwashes), 1–3 m of friction in a short pipe run and 0.5–1 m up to the return jets. The defaults in our calculator for a standard domestic pool add up to about 7 metres.
This is why two pumps with the same headline flow can perform very differently, and why sizing on flow alone leaves many pools short. The number that matters is the flow at your head, which you read from the pump curve.
Working out total head by hand is fiddly, so our pool pump calculator does it for you. You choose your power supply, enter your pool dimensions and turnover period, and adjust the four head figures above to match your installation. It then works out the flow and head you need and lists the pumps from our range that meet both. Use the Open pool calculator button near the top of our swimming pool pumps page, or scroll below the range. For long pipe runs, our Water Pump Performance Calculator estimates the friction losses in more detail. The results are indicative, so confirm the flow at your head on the pump curve before you buy.
Choosing the right pump for your pool
- Size on flow, not horsepower. Horsepower and kilowatts tell you how much power the motor draws, not how much water reaches the filter.
- Do not oversize. An oversized pump costs more to run, can push water through the filter too fast to clean it, and strains the seals. Choose the smallest pump that comfortably meets your flow and head.
- Check the filter. The pump must not exceed your filter's maximum flow rating, so check the rating on the filter before you choose a bigger pump.
- Match the connections. Most domestic pool pumps use 1.5 inch (50mm) or 2 inch (63mm) unions. Matching your pipework keeps installation simple, and adaptors usually bridge any difference.
- Check your supply. Most homes have a 230V single phase supply. Three phase (400V) versions of the Plastica Argonaut AV, Speroni SWIMM and Pentair Sta-Rite suit larger and commercial pools where a three phase supply is available.
- Salt pools. Salt chlorinated water corrodes pumps not built for it. Choose the ESPA Repospool, Plastica AG or Plastica Argonaut AV.
- Pump above the water level? Choose a pump that self-primes far enough. The Plastica AG self-primes up to 1.8 m of suction lift and the Argonaut AV up to 3 m.
Which pump suits which pool
These are starting points from our range. Maximum flow is measured at zero head and maximum head at zero flow, and the flow you actually get sits between the two on the pump curve.
| Pump | Best for | Maximum flow | Maximum head |
|---|---|---|---|
| Plastica iFlo (SFP075 to SFP150) | Best value for smaller domestic pools | 166–283 L/min | 10–17.5 m |
| Plastica AG (AG8 to AG16) | Quietest (around 55dB); above-ground and ornamental pools; salt-safe | 150–266 L/min | 8–13 m |
| Speroni SWIMM (500 to 4000T) | High-head systems with long pipe runs, heat pumps or sand filters | 250–450 L/min | 11–24 m |
| Plastica Argonaut AV (AV50 to AV250) | Pools over about 60,000 litres, long daily run times and commercial pools; salt-safe | 216–533 L/min | 11–18 m |
We also stock the variable speed Pentair Swimmey VSE for the lowest running cost, the heavy-duty Pentair Sta-Rite, the self-priming Pentair Freeflo and the ESPA Repospool for salt pools. Our guide to the best swimming pool pumps explains when to choose each one, and our guide to the Plastica range compares the iFlo, AG and Argonaut.
Emptying a pool rather than circulating it? That needs a drainage pump, not a pool pump. Our Swimming Pool Draining Pump Kit is built for the job.
Replacing an existing pump?
If your old pump ran reliably for years, match the flow, head, voltage, connection size and power on its data plate. If it always struggled to keep the pool clear, treat the replacement as a chance to size it properly rather than repeat the original mistake. Our guide on how to replace a swimming pool pump covers the warning signs and which figures to note, and you can send us a photo of the plate so we can match a replacement from the data plate.
Video: how to choose a swimming pool pump
More pool pump guides
- Best swimming pool pumps by use
- Pool pump running costs and how to reduce them
- How to replace a swimming pool pump
- Understanding the Plastica range of swimming pool pumps
- Understanding the Plastica Argonaut AV range
- How to build a swimming pool
- How to read a pump curve
- What size water pump do I need?
