01
The purpose
What does this calculator estimate?
Find the right pump horsepower for your flow and head — and see how much a variable-speed model would save.
Pumps & Filtration · C6
Pool Pump Sizing Calculator
Find the right pump horsepower for your flow and head — and see how much a variable-speed model would save.
Measure the inputsBigger isn't better — an oversized pump exceeds safe pipe velocity and wastes power.
Read the full resultSize to flow at your actual TDH, never to the pump's headline 'max flow' figure.
Check the boundaryA variable-speed pump almost always beats single-speed on lifetime cost — often by hundreds a year.
Useful forPumps & FiltrationPlanningComparisonVerification
Live calculation
Pump sizing inputs
✓ Checked May 2026
Enter flow, head, and pool type.
Sizing recommendation
—
Enter pool volume, total dynamic head and desired flow to size the pump.
Enter the known values. Let the engine handle the calculation.
✓ Formula checked↻ Live result○ No account needed
Planning estimate only. Confirm product labels, equipment specifications, qualified-professional advice and local requirements before acting.
The result, explained
Use the Pool Pump Sizing Calculator result with context.
Find the right pump horsepower for your flow and head — and see how much a variable-speed model would save.
02
The tool
What information does it use?
- Pool volume: enter a measured or verified value
- Total dynamic head: From the TDH calculator, in feet.
- Desired flow rate: Target GPM for your turnover goal.
- Pool type: Residential, commercial, spa, or above-ground.
03
The method
How to use this calculator
- Pool volumeEnter the value you can verify.
- Total dynamic headFrom the TDH calculator, in feet.
- Desired flow rateTarget GPM for your turnover goal.
- Pool typeResidential, commercial, spa, or above-ground.
04
The relationship
The formula in plain English
Choose the smallest pump whose flow curve delivers your GPM at your TDH
~1 HP ≈ 60 GPM @ 40 ft; 1.5 HP ≈ 80 GPM @ 50 ft; 2 HP ≈ 100 GPM @ 60 ft.05
Worked through
A worked example: 60 GPM needed at 40 ft TDH, residential
- Find smallest pump giving 60 GPM @ 40 ft head
- That's about a 1.0 HP single-speed
- A VSP at 50% speed would draw ~12.5% of full power
| Flow needed | At 30 ft TDH | At 50 ft TDH | At 70 ft TDH |
|---|---|---|---|
| 40 GPM | 0.5 HP | 0.75 HP | 1.0 HP |
| 60 GPM | 0.75 HP | 1.0 HP | 1.5 HP |
| 80 GPM | 1.0 HP | 1.5 HP | 2.0 HP |
| 100 GPM | 1.5 HP | 2.0 HP | 3.0 HP |
| 140 GPM | 2.0 HP | 3.0 HP | 3.0+ HP |
06
Why it matters
How the result supports the next decision
Bigger isn't better — an oversized pump exceeds safe pipe velocity and wastes power.
Size to flow at your actual TDH, never to the pump's headline 'max flow' figure.
07
Good inputs
Improve the estimate before relying on it
- Bigger isn't better — an oversized pump exceeds safe pipe velocity and wastes power.
- Size to flow at your actual TDH, never to the pump's headline 'max flow' figure.
- A variable-speed pump almost always beats single-speed on lifetime cost — often by hundreds a year.
- Match the pump to your filter and pipe; a too-big pump can damage cartridge filters.
- Many regions now mandate variable-speed pumps above a certain horsepower — check local code.
08
The boundary
How to interpret the result
Measurements, equipment specifications, site conditions and local requirements can change the practical result.
The engine reports invalid inputs and safety warnings beside the result. Resolve those messages before using the estimate.
09
Before acting
What should override this estimate?
- Measured site conditions and current test results
- Product labels and manufacturer specifications
- Qualified-professional advice and applicable local codes
10
Common questions
Frequently asked questions
What size pump do I need for my pool?
Pick the smallest pump that delivers your required flow rate at your system's total dynamic head. For a typical residential pool needing about 60 GPM at 40 feet of head, a 1 HP pump suffices. Sizing to flow-at-head, rather than to a pump's maximum flow, prevents the common mistake of oversizing.
Is a bigger pool pump better?
No. An oversized pump pushes water faster than your plumbing can safely handle, creating noise, erosion, cavitation risk, and wasted electricity — without cleaner water. It can also exceed a cartridge filter's rated flow and shorten its life. The right pump matches your flow goal at your head, no more.
Should I get a variable-speed pump?
For most pools, yes. Because pump power follows the cube of speed, running a variable-speed pump at half speed uses only about an eighth of the energy. Even though it costs more upfront, the savings typically pay it back in one to three years, and many areas now require them above a certain horsepower.
How does total dynamic head affect pump choice?
A pump's flow drops as head rises, so the same pump delivers different GPM in different systems. You must read the pump's performance curve at your calculated TDH to know the real flow you'll get. Two pools needing identical GPM may need different pumps if their head differs.
What horsepower for a spa or above-ground pool?
Spas need higher flow for jets but small volume, so they often use a dedicated higher-flow pump sized to the jet count. Above-ground pools have low head and modest volume, so a small pump — often ½ to 1 HP — is plenty. Always size to that specific system's flow and head.
What HP pump for a 15,000 gallon pool?
Around 1 HP for a typical 60 GPM target at 40 feet of head; confirm against your actual TDH.
Why is my pool pump so loud?
Often because it's oversized for the plumbing, pushing water past safe velocity. Right-sizing or slowing a VSP fixes it.
Do variable-speed pumps save money?
Yes — substantially. Running at low speed uses a fraction of the power, often paying back the upgrade in 1–3 years.
Primary sources
Use the result with current guidance.
These official references support safe planning context. Product labels, local requirements and qualified-professional advice take priority over a general calculator estimate.