Generator Wattage Calculator: What Size Generator Do You Need?
Buy a generator that is too small and it trips the moment your fridge kicks on. Buy one too big and you pay for fuel and noise you never use. This calculator gets you the right size in about a minute.
Tick what you want running at the same time. You get your running watts, your starting surge and the size to shop for.
Generator Wattage Calculator
Tick what you need to run at the same time. You get the running load, the starting surge and the generator size to buy.
Wattages are typical figures from generator maker sizing charts. Your appliance’s nameplate or manual is the real number: watts, or volts times amps. The recommendation adds 20 percent headroom so the generator is not run flat out.
Running Watts vs Starting Watts
Running watts are what your gear draws once it is up to speed. Starting watts are the short surge a motor needs to get moving, often two to three times its running draw.
You only need room for one surge at a time if you start motors one by one. That is why the calculator adds just the biggest surge on top of your running total.
How to Read Your Own Appliance
- Look for a watts figure on the nameplate or in the manual.
- If you only see volts and amps, multiply them. 120 volts times 5 amps is 600 watts.
- For starting watts, check the manual or use the typical figure in the list above.
Next Steps
Running power tools off a generator? Check your cord with the extension cord gauge calculator so long runs do not starve your motors. Then use the tool finder to match gear to your project.
Frequently Asked Questions
What size generator do I need to run a house?
For the basics, a refrigerator, sump pump, furnace fan, lights and electronics, you usually land between 5,000 and 7,500 running watts. Central air or an electric water heater pushes you much higher. Tick your items above for your own number.
Why add 20 percent headroom?
Generators run hotter, louder and less efficiently near their limit. Headroom keeps them in a comfortable range and leaves room for something you forgot.
Can I plug a generator into my house?
Not through an outlet. Use a transfer switch or interlock installed by a licensed electrician, which stops power from feeding back into the grid.
Is an inverter generator better?
For small loads and electronics, yes. Inverter generators are quieter and produce cleaner power. For big home backup loads, a conventional portable or standby unit is usually better value.