What Size Pool Pump Do You Need? An Easy Sizing Guide

August 7, 2025

If you’re looking to get a pool pump, you should choose the right one, as selecting the wrong pool pump size can waste energy, damage equipment, or leave your pool cloudy. In this blog, you’ll learn the step-by-step method of how to size a pool pump, common mistakes, and various tips to save energy.

A collage of four different types of swimming pool pumps, including single-speed and variable-speed models, on a white background.

Why Pool Pump Size Matters

It’s essential to choose the correct pool pump size. An oversized pump wastes energy, and an undersized one leads to poor filtration, algae growth, and cloudy water. Hence, getting the rightly sized pool pumps saves energy and ensures proper filtration.

How to Size a Pool Pump (Step-by-Step Guide)

Sizing a pool pump isn’t hard. Follow the steps below to correctly measure your pool pump size and get an appropriate one for your pool.

Step 1: Calculate Your Pool’s Volume

Find out your pool’s volume (in gallons) to calculate its water capacity.

An aerial view collage of three different pool shapes—rectangular, circular, and free-form—illustrating how to calculate pool volume for pump sizing.

For a rectangular pool, use: Length × Width × Average Depth × 7.5.
For a circular pool, use: Diameter × Diameter × Average Depth × 5.9.
For irregular shapes, try an online pool volume calculator.

For example, A 20’ × 40’ rectangular pool with a 5’ average depth holds 20 × 40 × 5 × 7.5 = 30,000 gallons.

Step 2: Find Out the Turnover Rate

Most residential pools need a full water turnover every 6 to 8 hours to ensure effective filtration. This helps keep the water clean. Your pump should be able to move the full amount of pool water in that time.

For example, for a 30,000-gallon pool, aim for a complete turnover in 8 hours to keep water clean.

Step 3: Calculate the Flow Rate (GPM)

To find the flow rate (in GPM), divide your pool’s gallons by the number of hours for turnover, then divide by 60. If you use a pool cleaner (e.g., a pressure cleaner needing 25 GPM), add its required GPM.

For example, for a 30,000-gallon pool with an 8-hour turnover,

30,000 ÷ 8 ÷ 60 = 62.5 GPM.

With a 25 GPM cleaner, total flow is 62.5 + 25 = 87.5 GPM. This ensures your pool pump size meets all needs.

Step 4: Find Out Total Dynamic Head (TDH)

TDH (Total Dynamic Head) shows how much resistance your pump works against from pipes, filters, and other parts. Most home pools have 30–60 feet of TDH. Pool cleaners or extra skimmers can add 5–15 feet.

Check your pump’s performance chart to see if it can give the needed flow (GPM) at your TDH. For best results, ask a pool expert to measure it.

Step 5: Choose the Right Horsepower (HP)

Use your GPM and TDH to find the right pump using a sizing chart (see below). Most home pools use pumps between 0.5 and 3 HP. Variable-speed pumps are great because they adjust the flow and save energy, making them perfect for use with a pool cleaner.

Example: For 87.5 GPM at 40 feet TDH, a 1.5 HP variable-speed pump could be a good fit. Just make sure it works with your filter to prevent damage.

Pro Tip: Download our free pool pump sizing checklist to simplify the process. Still unsure? Drop your pool size and gear in the comments, we’ll help you out!

Pool Pump Size Chart for Easy Reference

Picking the right pool pump size can seem tricky, but our easy-to-use pump size chart makes it simple.

Pool Volume (Gallons)	Turnover (Hours)	Min. Flow Rate (GPM)	Single-Speed HP	Variable-Speed HP
10,000–15,000	6–8	21–42	0.5–0.75	0.5–1.0
15,000–25,000	6–8	31–69	0.75–1.0	1.0–1.5
25,000–40,000	6–8	52–111	1.0–1.5	1.5–2.0
40,000+	6–8	83–167	1.5–3.0	2.0–3.0

Match your pool’s volume to the GPM and HP columns. Always confirm Total Dynamic Head (TDH) and filter compatibility.

Key Factors That Affect Pool Pump Size

Here are some of the factors that affect pool pump size.

A large, portable pool pump and filter system on a cart, returning clean, filtered water to a swimming pool to demonstrate water turnover.

Plumbing Size: Smaller pipes require a smaller pool pump size to avoid pressure issues and vice versa.
Filter Compatibility: Note that filters have max GPM ratings. Warning: A pump exceeding your filter’s GPM can cause damage.
Energy Efficiency: According to NREL (National Renewable Energy Laboratory), variable-speed pumps can save up to 90% on energy costs compared to single-speed models.
Pool Cleaner Type: The pressure or suction pool cleaners typically rely on the pump’s suction or return flow, adding 5–15 feet of TDH. You won't have this trouble if you are using a cordless pool cleaner.

Conclusion

Determining the ideal pool pump size is straightforward with the right steps. By calculating your pool’s volume, flow rate (GPM), and Total Dynamic Head (TDH), you can answer what size pool pump do I need with confidence.

For pools using robotic cleaners like the Dreame Z1 Pro, which operates cordlessly with 8,000 GPH suction for pools up to 2,160 square feet, the pump’s role shifts to supporting skimmers for surface debris since the cleaner doesn’t rely on pump flow.

Choosing the right pool pump size saves energy, reduces costs, and ensures thorough filtration for a sparkling clean pool. Use our pool pump size chart to get started, or consult a pool professional for complex setups with cleaners or skimmers.