The sump pump size calculator is a crucial tool for determining the rightsized sump pump for your specific needs. By accurately measuring the water inflow rate into the sump pit, you can estimate the volume of water that would enter your pit during an hour of steady rain. Multiplying this number by a safety factor of 1.5 will give you the pumping capacity you require for your home or commercial property.
Measuring the Sump Water Inflow Rate
To determine the appropriate sump pump size, you’ll need to measure the water inflow rate into your sump pit. Here’s how to do it:

Measure the Depth of Water Entering the Pit: Use a ruler or tape measure to record the depth of water entering the sump pit over a 1minute period. Repeat this process several times, especially during periods of heavy rainfall, to get an accurate average.

Calculate the Volume of Water Entering the Pit: Assuming a standard sump pit size of 18 inches in diameter, you can calculate the volume of water entering the pit using the formula:
Volume (gallons) = Depth (inches) x 0.3
(the conversion factor for an 18inch diameter pit). 
Determine the Hourly Inflow Rate: Multiply the volume of water entering the pit per minute by 60 to get the hourly inflow rate. For example, if the pit receives 20 inches of water in 1 minute, the hourly inflow rate would be 20 inches x 0.3 x 60 = 360 gallons per hour.

Apply the Safety Factor: To ensure your sump pump can handle even the heaviest rainfall, multiply the hourly inflow rate by a safety factor of 1.5. In the example above, the recommended pump capacity would be 360 gallons per hour x 1.5 = 540 gallons per hour.
Considering the Vertical Lift Distance
When choosing a sump pump, it’s essential to consider the vertical lift distance, which is the height that the sump water must be pumped before leaving the house. A higher lift distance makes the pump work harder, reducing its pumping rate.
To calculate the vertical lift distance, measure the distance from the bottom of the sump pit to the point where the discharge pipe exits the home. This distance, combined with the water inflow rate, will determine the appropriate horsepower and pump capacity required for your system.
Measuring the Water Flow Rate and Necessary Capacity
In addition to the water inflow rate, you’ll need to measure the water flow rate and necessary pump capacity. Here’s how to do it:

Drain the Sump Pit: Run your pump until it fully drains the basin, then measure the depth of the standing water inside.

Measure the Water Accumulation: After waiting exactly 1 minute, measure the depth of the water again. Subtract the first measurement from the new depth to get the amount of water that accumulated in the basin.

Calculate the Gallons per Minute: Multiply the amount of water that accumulated in the basin in 1 minute by 60 to get the number of gallons that would collect in the basin in an hour.

Apply the Safety Factor: Multiply the gallons per hour by 1.5 as a safety factor to ensure the pump has sufficient power during heavy rainfall.
For example, if the basin accumulated 2 inches of water in 1 minute, the calculation would be:
* 2 inches x 0.3 (conversion factor) = 0.6 gallons
* 0.6 gallons x 60 minutes = 36 gallons per hour
* 36 gallons per hour x 1.5 (safety factor) = 54 gallons per hour
Selecting the Appropriate Sump Pump
Once you’ve calculated the water inflow rate, vertical lift distance, and necessary pump capacity, you can use this information to select the appropriate sump pump for your needs. Consider the following factors when choosing a sump pump:
 Pump Capacity: The pump capacity should be at least 1.5 times the calculated hourly inflow rate to account for heavy rainfall.
 Horsepower: The pump’s horsepower should be sufficient to overcome the vertical lift distance and provide the necessary flow rate.
 Pump Type: Choose between a pedestal or submersible sump pump based on your specific installation requirements and preferences.
 Backup Power: Consider a batterypowered backup sump pump to ensure your system continues to function during power outages.
Conclusion
The sump pump size calculator is a valuable tool for ensuring your home or commercial property is equipped with the rightsized sump pump to handle even the heaviest rainfall. By accurately measuring the water inflow rate, vertical lift distance, and necessary pump capacity, you can select a sump pump that will effectively and efficiently remove excess water from your sump pit, protecting your property from water damage.
References:
 Water Damage Defense – Sump Pump Size
 Apex Pros – How to Determine What Size of Sump Pump You Need
 Zoeller Pumps – Pump Sizing Program
The techiescience.com Core SME Team is a group of experienced subject matter experts from diverse scientific and technical fields including Physics, Chemistry, Technology,Electronics & Electrical Engineering, Automotive, Mechanical Engineering. Our team collaborates to create highquality, wellresearched articles on a wide range of science and technology topics for the techiescience.com website.
All Our Senior SME are having more than 7 Years of experience in the respective fields . They are either Working Industry Professionals or assocaited With different Universities. Refer Our Authors Page to get to know About our Core SMEs.