Pool Pump Sizing Calculator
A properly sized pump ensures adequate filtration and water clarity while minimizing energy costs. Oversized pumps waste electricity; undersized pumps cannot turn over the water fast enough to maintain safe chemistry. This calculator determines the minimum flow rate and pump horsepower for your pool.
Pool Parameters
Variable-speed pumps can run at lower GPM for longer hours, reducing energy costs by 60–80% vs. single-speed. Many states now require VS pumps on new installations per DOE efficiency standards (effective July 2021).
Pool Pump Sizing Formula
The fundamental formula for pool pump sizing:
Required GPM = Pool Volume (gallons) ÷ Turnover Time (hours) ÷ 60
Example: 15,000 gallon pool ÷ 8 hours ÷ 60 = 31.25 GPM minimum flow rate.
Maximum Flow Rates by Pipe Size
| Pipe Diameter | Max Safe Flow | Velocity at Max |
|---|---|---|
| 1.5 inch | 43 GPM | 8 ft/sec |
| 2.0 inch | 73 GPM | 8 ft/sec |
| 2.5 inch | 120 GPM | 8 ft/sec |
Pump HP vs. Flow Rate (Typical)
| Horsepower | Flow Rate (GPM) | Best For |
|---|---|---|
| 0.75 HP | 30–40 GPM | Small pools (<12,000 gal) |
| 1.0 HP | 40–55 GPM | Standard residential (12–20K gal) |
| 1.5 HP | 55–70 GPM | Larger pools (20–30K gal) |
| 2.0 HP | 70–85 GPM | Large pools / spa combos |
| 3.0 HP | 85–110 GPM | Commercial / water features |
Frequently Asked Questions
What happens if my pump is too big?
An oversized pump pushes water too fast through the filter, reducing filtration efficiency. It also wastes electricity — a 1.5 HP pump costs roughly $100–150/month to run 8 hours daily, while a right-sized VS pump at low speed costs $30–50/month for the same turnover.
How many hours per day should I run my pool pump?
Run the pump long enough to turn over the full volume at least once per day. For a VS pump at low speed, this may be 10–12 hours. For a single-speed pump, 8 hours is standard. Commercial pools require 6-hour turnover per health code.