Sump Pump Flow & Discharge Rates

Last Updated on by Anthony Brown

In order to prevent basement flooding you need to use the right size sump pump. Most sump pumps advertise horse power but this can be confusing. What you really need to know is your sump pump flow (discharge) rate to get the right pump!

Not sure what the flow rate of your sump pump. Not many people know their pumps discharge rate – or how to calculate it! Fortunately all you need to calculate flow rate is a tape measure, a timer and a bucket of water.

How to Measure Flow Rate

Ready to get started measuring your sump pump flow rate. Most instruction manuals have flow rate tables but if you lost the papers follow these step by step instructions. 

Start by determining the amount of water entering the pit every minute. Second, measure how high you need to move the water (aka the head height). Once you know all the numbers it is easy to pick the right size pump – remember higher flow rates mean more horse power.

How to Increase Flow Rate

Does your pump look like it is struggling to clear the water in the pit – you might need to increase the flow rate. Your pump probably advertised a maximum flow rate, but that does not mean it is currently operating at peak efficiency.

Flow Rate Formula

Want to calculate your pump capacity. Use this formula – 

Inches of Water x 60 Minutes x 1.5 = Gallons per Hour

Pump Flow Rate Table

Pit DiameterGallons of Water
24"2
30"3
36"4
42"6
48"7.5
60"12
72"17.5

Zoeller Sump Pump Flow Rate

Zoeller makes some of our favorite pumps on the market. We did the research and put together everything you need to know about their flow and discharge rates! Use the chart below to help decide which pump is right for your home based on water flow.

PumpMotorMax HeadMax Flow Rate
50 Series3/10 HP19.25' (5.9 m)43 GPM (163 LPM)
Model 633/10 HP 19.25' (5.9 m)43 GPM (163 LPM)
Model 723/10 HP 18' (5.5 m)38 GPM (144 LPM)
Model 731/3 HP 18' (5.5 m)38 GPM (144 LPM)
Model 751/2 HP25' (7.6 m)50 GPM (189 LPM)
Model 761/2 HP25' (7.6 m)50 GPM (189 LPM)
Model 951/2 HP26' (7.9 m)80 GPM (303 LPM)
Model 981/2 HP23' (7 m)72 GPM (273 LPM)