With generators, the most important factor is size. Portable generators are sized according to watt output, and you want enough watts to power what you need but not so much that you're wasting power. Power usage and generator sizes are measured in watts. To size a generator, you'll have to anticipate how much power you're going to need, and then find a generator that meets these demands.
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Decide what you want to run on the portable generator. You may only want to run essential items like your refrigerator and cooking appliances, or you may want to run those in addition to the television and other entertainment devices. Either way, you will need to consider everything you plan on running to properly size a generator.
Check the watt usage of each of the items you want to run. Appliances like microwaves will often list the amount of watts they use somewhere on them, and you can find power usage in the documentation that comes with electronic devices. You can also contact the manufacturer for information on a particular device if you can't find power usage information among your owner's manuals.
Add the watt usage for each of the items together to determine the total watt output you need.
Get a generator that fits your power needs. If your watt usage falls between the watt output of two generators, get the larger of the two. This will account for fluctuating power needs.