*Recommended: Round up to the nearest standard motor size (e.g., 0.5, 0.75, 1.0, 1.5 HP).
How to Determine the Right Water Pump Size
Choosing the correct water pump is critical for ensuring adequate pressure and flow while maintaining the longevity of the pump motor. An undersized pump will fail to meet your pressure needs, while an oversized pump wastes energy and can cause "short-cycling," which burns out the motor prematurely.
Key Variables in Pump Sizing
Flow Rate (GPM): This is how much water you need per minute. A standard residential home typically requires 7 to 12 Gallons Per Minute (GPM).
Static Head: The vertical distance water must be lifted. If your well is 50 feet deep and your tank is at ground level, your static head is 50 feet.
Friction Loss: As water moves through pipes, it loses energy due to friction against the pipe walls. This is influenced by pipe diameter, material, and length. (This calculator estimates a standard 5% loss for general calculations).
Discharge Pressure (PSI): The "push" required at the end of the line. For a standard home pressure tank, this is usually 40 to 60 PSI. Note that 1 PSI = 2.31 feet of head.
Practical Example: Sizing for a Garden Well
Imagine you have a well where the water level is 30 feet below the surface. You want to pump water to a garden 100 feet away and maintain 30 PSI for a sprinkler system at a rate of 5 GPM.