What Size Generator to Run Sump Pump? – [Detailed Guide]

During extended blackouts, the generator is the only machine to save your basement from the creepy flood.

Before making a buying decision we must have a better understanding of what size generator we need to run the sump pump smoothly. What are the different sizes available in the market? And how can we calculate the wattages of a sump pump?

In this article, we are going to provide you with detailed answers to what things should be considered before getting a generator for the sump pump? what are some easy ways to calculate the wattages? and a table of different sump pumps with their power ratings as well.

Without further wasting time let’s dive in.

A 2000-watt generator could run a sump pump of normal horsepower (1/2, 1/3,1/4) smoothly but we suggest you get a bigger one (4000 – 5000 wattages) for better performance. Additionally, you can operate other appliances like refrigerator, microwave, etc., simultaneously with the sump pump without overloading the generator.

How Many Amps/wattages Does a Sump Pump Use?

Sump Pump SizesWattagesAmps
1 hp Sump Pump2,00010
½ hp Sump Pump1000-1050
¾ hp Sump Pump1,5008
¼ hp Sump Pump550-6003.5-3.8
1/3 hp Sump Pump800 – 9003. 8 – 4

Before starting the calculation let’s understand what are the starting and running watts.

Starting watts: The amount of wattage a sump pump or other mother machines needs for initial startup.

Running watts: The amount of wattage a sump pump or other mother machines needs for constant running they are generally lower than the starting watts.

What Size Generator to Run Sump Pump? -[How to Pick A Right Size?]

What Size Generator to Run Sump Pump?

The following things should be kept in mind before getting a generator for the sump pump

Power Ratings (starting and Running Watts):

Like all electronic appliances a sump pump also has starting and running wattages, you should have to know that before making a buying decision.

You can check out the wattage/power ratings from the energy label (particularly in Yellow color) of the sump pumps containing the frequency, amps, voltage, Horsepower, etc.

Also, you can go through their user manual or use devices like Multimeter to calculate the accurate wattages/amps your sump pump is using.

Below is a detailed example of how I am doing the calculations.

I.e. I have a 120 voltage sump pump with 10 running and 15 starting amps, since every generator has wattage readings we have to convert the provided amps in wattages by using the power formula.

Watt = Amp X Volt

  • Watts = 10 x 120 = 1200 watts for running
  • Watts= 15 x 1800 watts for starting

Now we have the expected wattage rating of the sump going to draw. Also, we need to add 10 – 20% extra wattage because of the power losses.

As per the above example, a 2000-wattage generator could be enough.

The Number of Sump Pumps You Are Going to Operate:

If you are going to operate the multiple sump pumps you have to calculate the wattages/amps of each and sum them to get the actual wattages they are going to consume.

Do You Want to Use Other Appliances?

Sump pump with other appliances

Like the number of sump pumps, if you are going to operate the other appliance like a refrigerator, Air conditioner, microwave, etc. simultaneously with the sump pump,  you have to calculate the wattages of each appliance and choose the generator accordingly.

We have written a detailed guide about the generator sizing for every house with a bunch of appliances as well, make sure to have a look.

Are you using Older Models of a Sump Pump?

If your sump pump is based on older technology it will draw more wattages/amps compared to the newer one.

As the newer models are more energy efficient with the latest LVS (low voltage Series) or even with inverter technologies to cut off your monthly electricity bill.

Recommended Guide: What Size Generator to Run a Furnace?

Why Do I Need a Generator For My Sump Pump?

During the extended blackout, many users are crying that our sump pump stops working, and lots of floods and mess accumulated in our basement which is strange.

The most secure way is to get a generator to power the sump pump for a longer duration. During the power outages, I mostly powered my sump pump with a 4000 watts generator and surprisingly it is providing me 8 hours of run time with a single tank of 3 gallons.

Wrapping – Up

We highly recommend our readers do calculations before getting a generator for the sump pump. You can find the actual power ratings of a sump pump in the user manual or the energy label (usually in yellow color).

Additionally, we have written a whole section about how to pick the right-sized generator for a sump pump? You just need to skim it for a better understanding.

FAQs – Frequently Asked Questions

Can a Solar Generator Power a Sump Pump?

Yes, if the solar generator has enough starting and running wattages, I am running a 1Hp Sump pump on Ecoflow delta pro solar generator with 3600 running and 7000 surge wattages. You can easily run a normal sump pump with a 2000-wattage solar generator.

What size generator for 2 sump pumps?

Depending on the sizes of sump pumps, if you have pair of 1/2Hp you should have at least a 5000-wattage generator. Also if you have older sump pumps with higher starting and running wattage, you have to get the bigger one.

Will a 2000-watt generator run a sump pump?

A 2000 watts generator could run a lower powered sump pump like 1/4, or 1/3. However, you must have at least 3500 – 5000 wattage generators for the bigger powerful sump pump.

Will a 1000-watt generator run a sump pump?

Since a normal sump pump of the lowest power has higher starting wattages than a 1000-watt generator. We recommend getting at least a 2000 watts generator for a lower-power sump pump.

What Is The Right Size Generator To Run A 1/3 HP Sump Pump?

Since a normal sump pump of 1/3Hp draws 800 – 900 of running and 1400 – 1800 wattages depending on the model and brand, a 2000-wattage generator could run it smoothly unless your sump pump is too old and need higher starting power.

josh Milan


Josh is a highly skilled electrician with specialized expertise in the field of generators. With years of experience under his belt, he has established himself as an expert in all aspects of generators, ranging from installation and maintenance to troubleshooting and repairs. Josh’s in-depth knowledge of electrical systems and his commitment to staying updated with the latest industry advancements make him a reliable and sought-after professional.

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