Generator for Sump Pump: Sizing and Runtime
Short answer: To power a sump pump during a storm, you need a generator that can handle the pump's starting watts, which are higher than its running watts. Look for a generator with a starting watt rating that exceeds the pump's starting requirement. Runtime depends on fuel capacity and load, so check the maker's stated runtime at the load you expect. Always run the generator outdoors, far from windows and doors, per CPSC guidance.
Understanding sump pump power needs
A sump pump has two power figures: running watts and starting watts. Running watts are what the pump uses to operate continuously. Starting watts, also called surge watts, are the extra power needed for a fraction of a second when the motor starts. The starting figure is always higher.
When you read a generator listing, the first watt figure is often the starting watts, and the second is the running watts. For a sump pump, the generator's starting watts must be at least as high as the pump's starting watts. If the generator cannot deliver that surge, the pump may not start.
The pump's exact figures are on its nameplate or in its manual. The generator's figures are on its listing and in the maker's specifications. Compare the two directly. For more on reading watt figures, see how to read running and starting watts.
Reading generator listings for sump pump use
Generator listings state the starting and running watts in the title or the bullet list. A title that reads '3,000 starting watts, 2,500 running watts' tells you the surge capability and the continuous capability. For a sump pump, you need the starting watts to cover the pump's surge.
Some listings show only one watt figure. If the listing does not state both figures, check the maker's page for the full specification. The site's guides compare stated details, so you can see which listings give both numbers.
The type of generator matters too. Inverter generators and conventional open-frame generators both list starting and running watts. The difference is in how they deliver power, not in the watt figures themselves. Read the listing to see which type you are looking at. See inverter vs conventional for more.
Runtime considerations
Runtime is how long a generator runs on a full tank of fuel at a given load. Listings often state runtime at a specific load, such as half load or full load. For a sump pump, the load is the pump's running watts, which is usually a fraction of the generator's capacity.
A generator with a larger fuel tank generally runs longer, but the actual runtime depends on the load. The maker's page will state runtime figures for different loads. Use the figure that matches your pump's running watts to estimate how long the generator will run before you need to refuel. Learn more about runtime at half load.
During a storm, you may need to run the generator for hours. Consider the runtime at the load you expect, and plan for refueling. The generator's fuel gauge, if it has one, helps you monitor the level. See fuel tank capacity for details.
Matching generator size to pump
The generator's starting watts must exceed the pump's starting watts. If the pump's starting watts are, for example, 2,200, a generator with 3,000 starting watts leaves margin. If the pump's starting watts are higher, you need a larger generator.
The generator's running watts must also exceed the pump's running watts for continuous operation. A pump that runs at 800 watts needs a generator with at least 800 running watts, but the starting watts are the limiting factor.
If you plan to power other items during an outage, add their starting watts to the pump's starting watts. The generator must handle the combined surge. The site's guides group generators by watt range, so you can filter by the starting watts you need. See home backup sizing for more.
Safety and carbon monoxide
Generators produce carbon monoxide, a colorless, odorless gas that can be deadly. The CPSC warns that one generator produces as much CO as hundreds of cars, and it can kill you in minutes. Never use a portable generator indoors, in garages, basements, or sheds. Always use it outside, far from windows, doors, and vents.
Follow the maker's manual for safe operation, and read the CPSC, CDC, and NFPA carbon monoxide pages for guidance. Install battery-operated CO alarms in your home, per the CPSC's advice. See the sources below for official guidance.
This site does not give placement advice beyond pointing to the official sources. The CPSC and CDC pages in the sources below explain the details.
What to pick for your situation
For a sump pump, the key is to match the generator's starting watts to the pump's surge. A small inverter generator in the 2,000 to 3,000 watt range may be enough for a typical pump, but check the pump's figures. A larger conventional generator in the 3,000 to 5,000 watt range gives more margin and can power additional items.
Consider the fuel type. Gasoline is common, but dual fuel and tri fuel generators offer flexibility. The fuel choice affects runtime and availability, so think about what you can store and access during a storm. See fuel types comparison for more.
Use the site's guides to compare generators by stated details, including starting watts, running watts, and runtime. The guides are organized by watt range and fuel type, so you can narrow down the options.
What to pick for your situation
| If you | Pick | Buying guide |
|---|---|---|
| You need a generator mainly for a sump pump and a few small items | A portable generator in the 3,000 to 5,000 watt range | Best 3000 to 5000 Watt Generators: 13 Picks by Stated Details |
| You want a generator with extra capacity for other appliances during outages | A generator in the 5,001 to 9,000 watt range | Best 5001 to 9000 Watt Generators 2026: 9 Picks by Stated Details |
| You prefer a quieter, more compact option for occasional use | An inverter generator | Best Inverter Generator in 2026: 15 Picks by Stated Details |
| You want the flexibility of running on gasoline or propane | A dual fuel generator | Best Dual Fuel Generators in 2026: 15 Picks by Stated Details |
| You want the option of natural gas as well as gasoline and propane | A tri fuel generator | Best Tri Fuel Generators in 2026: 15 Picks by Stated Details |
| You are shopping on a tight budget | A generator in the budget tier | Best Generator Under $500 (2026): 5 Picks by Stated Details |
Questions
What size generator do I need for a sump pump?
The generator's starting watts must be higher than the pump's starting watts. Check the pump's nameplate for the starting figure and compare it to the generator's starting watts. A generator with at least 3,000 starting watts is a common starting point, but the exact size depends on your pump.
How long will a generator run a sump pump?
Runtime depends on the generator's fuel tank capacity and the load. The maker's page states runtime at specific loads. Use the runtime figure that matches your pump's running watts to estimate how long the generator will run before refueling.
Can I use a small inverter generator for a sump pump?
Yes, if the inverter generator's starting watts exceed the pump's starting watts. Many small inverter generators have starting watts in the 2,000 to 3,000 range, which may be enough for a typical pump. Check the pump's figures and the generator's stated starting watts.
Is it safe to run a generator in the garage during a storm?
No. The CPSC warns that generators produce deadly carbon monoxide and should never be used indoors, in garages, basements, or sheds. Always run the generator outside, far from windows, doors, and vents.
What does 'starting watts' mean on a generator listing?
Starting watts, also called surge watts, is the extra power a generator can deliver for a short time when a motor starts. It is higher than the running watts. For a sump pump, the generator's starting watts must cover the pump's starting surge.
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