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Use our pool pump size calculator to find the flow rate your pool needs. Calculate pool volume, GPM, and turnover time with ease.
| Step | Formula |
|---|---|
| Rectangular volume (ft) | Volume (gal) = L x W x avgDepth x 7.48052 |
| Rectangular volume (m) | Volume (gal) = L x W x avgDepth x 264.172052 |
| Circular volume | Volume (gal) = PI x r^2 x avgDepth x (7.48052 ft | 264.172052 m), r = Diameter / 2 |
| Average depth | avgDepth = (Shallow-End + Deep-End) / 2 |
| Required flow | GPM = Volume (US gal) / (Turnover Hours x 60) |
| Actual turnover time | Hours = Volume (US gal) / (Actual GPM x 60) |
A pool pump keeps water moving through your filter. The right size helps your pool stay clean and clear. A pump that's too small may not move enough water. One that's too large may waste power.
Our pool pump size calculator helps you find the flow rate your pool needs. Enter your pool size and target turnover time. Then, get your required flow in gallons per minute (GPM). You can also view other flow units.
A pool pump size calculator finds the flow rate needed to move your pool water within a set time. It uses pool volume and target turnover time.
Think of your pool like a big tank. The pump moves water through a filter, much like a fan moves air through a room.
The result gives you a starting point for pump selection. You must also check pipe size, filter limits, and total dynamic head (TDH).
Use this simple formula to find the flow rate your pool needs.
Required GPM = Pool Volume in US Gallons ÷ (Turnover Time in Hours × 60)
GPM means gallons per minute. Turnover time is the time needed to move one pool volume through the system.
For a rectangular pool, use this formula:
Pool Volume = Length × Width × Average Depth × 7.48052
Use feet for all three measures. The result is in US gallons.
For a round pool, use:
Pool Volume = 3.14159 × Radius × Radius × Average Depth × 7.48052
Radius is half the pool's diameter.
If you use meters, first find the pool volume in cubic meters. Then multiply it by 264.172 to get US gallons.
Follow these five simple steps to find your required flow rate.
Choose a method. Enter your pool size or type in its total volume.
Enter pool details. Add the length, width, diameter, and depth as needed.
Set turnover time. Enter your target time in hours.
Choose an output unit. View the result in GPM, GPH, L/min, or m³/h.
Check your results. Review the flow rate and use it to help select a suitable pump.
The calculator does the math for you. You don't need to work through each formula by hand.
Suppose you have a pool with 20,000 US gallons of water. You want to turn over the water in eight hours.
First, multiply eight hours by 60 minutes.
8 × 60 = 480 minutes
Next, divide the pool volume by 480.
20,000 ÷ 480 = 41.67 GPM
Your pool needs a target flow of about 41.67 GPM.
This equals 2,500 GPH, or about 157.73 liters per minute. Think of this as your target, not a promise of real pump output.
The pump must deliver this flow at your system's actual TDH. Check the pump curve and filter limits before you buy.
Use this quick chart as a guide. It shows the flow needed for an eight-hour turnover.
| Pool volume (US gallons) | Required flow (GPM) |
5,000 | 10.42 |
10,000 | 20.83 |
15,000 | 31.25 |
20,000 | 41.67 |
25,000 | 52.08 |
30,000 | 62.50 |
These are target flow rates, not fixed pump sizes. Your plumbing and filter can change the flow your pump can deliver.
For pools measured in litres, use this formula:
Required L/min = Pool Volume in Litres ÷ (Turnover Hours × 60)
For example, a 75,000-litre pool with an eight-hour turnover needs:
75,000 ÷ (8 × 60) = 156.25 L/min
This is a useful starting point for pools outside the USA.
An above-ground pool uses the same basic flow formula as an in-ground pool. Enter the pool volume and target turnover time to find the required flow.
Also check the filter rating, hose size, and pump curve. These help you choose a pump that fits your pool system.
Our pool pump size calculator helps you find the flow rate your pool needs. It works with pool dimensions or a known volume. It also converts results into common flow units.
Use the result as your starting point. Check TDH, pipe limits, and filter ratings before you choose a pump. The right match can help your pool run well without wasting power.
Find your pool volume first. Divide it by your target turnover time in minutes. Then check the pump curve to find a model that can deliver that flow at your system's TDH.
For an eight-hour turnover, you need about 41.67 GPM. The final pump choice depends on your plumbing and filter.
Usually, yes. A larger pool often needs more flow to meet the same turnover time. But pipe size and system resistance also matter.
Yes. Enter the pool volume or its dimensions. The same flow formula works for both above-ground and in-ground pools.
Multiply GPM by 3.78541. For example, 10 GPM equals about 37.85 L/min.
No. Flow rate alone can't give an accurate horsepower rating. You also need TDH and the pump's performance curve.