A pool pump that is too small never clears the water. One that is too big wastes electricity every single day and can damage the filter.
Here is how to work out what size pool pump you need, in metric, for a South African pool.
What Size Pool Pump Do I Need?
Size the pump by turnover, which is the time it takes to push the whole pool through the filter once.
Aim to turn the pool over in 6 to 8 hours.
Required flow rate in m3/h = pool volume in m3 divided by turnover hours
A 40,000 litre pool is 40 m3. Over 8 hours that is 5 m3/h. Over 6 hours it is 6.7 m3/h.
Pool Pump Size Chart in Litres
| Pool volume | Flow needed (8 hr turnover) | Flow needed (6 hr turnover) | Typical pump |
|---|---|---|---|
| 20,000 L | 2.5 m3/h | 3.3 m3/h | 0.45 to 0.75 kW |
| 30,000 L | 3.75 m3/h | 5.0 m3/h | 0.75 kW |
| 40,000 L | 5.0 m3/h | 6.7 m3/h | 0.75 to 1.1 kW |
| 50,000 L | 6.25 m3/h | 8.3 m3/h | 1.1 kW |
| 60,000 L | 7.5 m3/h | 10.0 m3/h | 1.1 to 1.5 kW |
Pumps here are rated in kilowatts rather than horsepower. Treat the kW column as a starting point and match the actual flow curve to your filter.
Why Pool Pump Size Must Match the Filter
This is the mistake we see most often. A big pump on a small filter pushes water through the sand too fast to filter it properly, and can damage the filter internals.
The filter has a maximum flow rating. The pump must not exceed it.
- 3-bag sand filter: suits roughly 5 to 7 m3/h
- 4-bag sand filter: suits roughly 7 to 9 m3/h
- 5-bag sand filter: suits roughly 9 to 12 m3/h
Confirm against your filter plate. Oversizing the pump is the quickest way to ruin a good filter.
Signs Your Pool Pump Size Is Wrong
- Pump runs all day and the water still looks dull, so it is undersized
- Filter pressure sits high from the moment you start it, so it is oversized
- Sand blowing back into the pool, a sign of too much flow
- Electricity bill climbing with no change in run time
Pool Pump Sizing and Running Cost in South Africa
Pump size drives your electricity bill more than anything else at the pool.
A smaller pump running longer is usually cheaper than a large pump running briefly, because power draw rises steeply with motor size. A variable speed pump run slowly for longer is cheaper still.
With Eskom tariffs where they are, correct pump sizing pays for itself over a season.
How to Size a Pool Pump When You Do Not Know the Volume
You cannot size a pump without the volume. Work it out first using our pool volume guide, then come back to the flow table above.
Not Sure What Size Pool Pump You Need? We Will Measure It
We size pumps against your actual pool volume, filter rating and pipework, not a generic chart.
Our team tests and balances pool water across Cape Town and the Winelands. We work from a real reading, not a guess. Request a free quote or see our pool maintenance services.
If your current pump is noisy, leaking or short cycling, see our pool pump repairs in Cape Town.
