Pool pump size calculator
Pumps are sized by flow, not horsepower. Enter your volume and how fast you want the water turned over; the calculator gives the flow rate and checks it against your pipes.
Flow you need
Choosing the pump
Look at the pump’s performance curve and pick one that delivers 31 gpm at your system’s head. Typical residential in-ground systems run 40–60 ft of total dynamic head; add more for long runs, heaters, solar panels or spa jets. Check that the flow is within your filter’s rating using the filter size calculator.
Since 2021, US federal efficiency rules (DOE dedicated-purpose pool pump standards) effectively require variable-speed motors on most new in-ground pumps of 1 total horsepower and up.
Why one turnover doesn’t clean all the water
Filtered water flows back into the pool and mixes with water that hasn’t been filtered yet, so the pump keeps re-filtering clean water. The share cleaned follows 1 − e−n, where n is the number of turnovers.
63% filtered
Going from 2 to 3 turnovers only adds 9 points. This is why a slow, long run on a variable-speed pump is so much cheaper: pump power falls roughly with the cube of speed, while filtration only falls in proportion.
Max flow by pipe size
| Sched. 40 PVC | Suction (6 ft/s) | Return (8 ft/s) |
|---|---|---|
| 2 inch | 63 gpm | 84 gpm |
| 3 inch | 138 gpm | 184 gpm |
| 1.5 inch | 38 gpm | 51 gpm |
| 2.5 inch | 90 gpm | 119 gpm |
Velocity limits of 6 ft/s suction and 8 ft/s return are the values recommended in the ANSI/APSP-15 residential pump energy-efficiency standard.
Questions pool owners ask
What size pump do I need for my pool?
Work out the flow rate first: pool gallons ÷ turnover hours ÷ 60 gives gallons per minute. A 20,000 gallon pool turned over in 8 hours needs 42 gpm. Then choose a pump that delivers that flow at your system’s resistance (total dynamic head), usually 40–60 ft of head for a typical in-ground pool. A variable-speed pump lets you set the flow exactly.
How many hours a day should I run my pool pump?
Enough to turn the water over about once a day in most residential pools, often 8–12 hours on a single-speed pump. With a variable-speed pump, running longer at low speed filters the same water using far less electricity, because power drops roughly with the cube of speed.
What is pool turnover rate?
The time it takes to pump a volume equal to the whole pool through the filter. Because filtered water mixes back in, one turnover cleans only about 63% of the water; two turnovers about 86%, and three about 95%.
Can a pool pump be too big?
Yes. An oversized single-speed pump wastes electricity, can exceed your filter’s rated flow, and pushes water faster through pipes than recommended, which adds noise and wear. Match flow to your filter, heater and pipe size.
What is the maximum flow for 1.5 and 2 inch pipe?
At the commonly recommended velocities (about 6 ft/s on suction and 8 ft/s on return lines), 1.5 inch schedule 40 PVC carries about 38 gpm suction / 51 gpm return, and 2 inch about 63 / 84 gpm. Pumps connected to smaller plumbing can’t use their full rated flow.