How to Calculate Generator Wattage

When planning your generator purchase the first thing you’ll likely ask is, “How many watts do I need?” Or, “Will my 4000 watt generator run my air conditioner?” It’s not always an easy question to answer, but that’s where we come in. Below is a handy wattage calculator and step-by-step instructions to help you plan your next purchase.

What You’ll Need to Calculate Portable Generator Wattage

• List of household appliances and devices
• Running wattage for each appliance and device
• Starting wattage for any appliance or device with a motor

To help with your running wattage, we’ve included a list of approximate running wattage for various household appliances in our calculator. The power requirements listed are general examples and should not be used to calculate your specific power needs. Refer to the user manuals that came with your devices for manufacturer-provided power requirements.

Step-By-Step Instructions

1. Gather your list of household appliances and devices you wish to power with your generator.
2. Record the starting wattage for each item with a motor.
3. Note which device has the highest starting wattage.
4. Record the running wattage for app appliances and devices. Consult your user manuals for exact wattage.
5. We’ve included a list of various household appliances in our calculator. Go ahead and enter any wattage in the corresponding field.
6. If your device is not listed, include it in the ‘Other’ field.
7. In the field ‘Highest Starting Wattage,’ input the number you recorded in step three.
8. Your approximate wattage needs will show in below the ‘Your Total Wattage Needs’ heading.

What’s the difference between running wattage and starting wattage?

The running wattage is the amount of electricity needed to keep the device running. Appliances or devices without a motor, light bulbs, coffeemakers, cell phones, etc, don’t need extra power when they’re turned on, so you only need the running wattage for these.

Any appliance with a motor has a starting wattage in addition to the running wattage. The starting wattage is the amount of electricity you need to start the device. If you can’t find the starting wattage, a good rule of thumb is that the amount of power you need to start a device is usually three times the amount you need to keep it running.