How to Calculate Sump Size

Your home's sump pump is the last line of defense against a wet basement.

A correctly sized sump pump assures a dry basement.A correctly sized sump pump assures a dry basement.
In some houses, weeping tile on the exterior of the home and around the foundation's footings move water to the sump pit. The sump pump then pushes that water into a pipe where it is discharged away from the home. The pump needs to be sized correctly to handle the maximum amount of water during a heavy rainstorm.

Measure the width of your sump pit with a measuring tape.

Determine the number of inches of water that enter the sump pit during a heavy rain storm over a period of 60 seconds. For an 18-inch basin, one inch of water is equal to 1 gallon. For a 24-inch basin, 1 inch of water is about 2 gallons. This calculation will tell you the flow in gallons per minute (GPM).

Measure from the bottom of the sump pit to the maximum height of the discharge pipe. This is called the "static head."

Choose a pump that can handle the water flow GPM at the specific static head measurement for your house. Refer to the manufacturer's charts that show the pump's performance rate.

Things You Will Need

  • Measuring tape
  • Stop watch

Tip

  • You do not want a pump that is either too small or too powerful. If it is too small your basement will fill with water. If it is too powerful, the pump will frequently turn on and off, thereby shortening the life of the pump.

About the Author

Bob White began his writing career in 2006. Working in sales, he was a technical writer tasked with responding to requests for proposal. White has a Bachelor of Arts in computer science and a diploma in home inspection. He has also worked in construction, landscaping and the pool industry for more than 15 years.