How to size a generator for your home during an outage

The right generator for an outage is the one that runs what you truly need, not your whole house at full use. This walk-through helps you estimate wattage so a provider can recommend a unit.

Step 1: list the essentials

Write down what must run: refrigerator, freezer, a few lights, phone charging, a well pump, a furnace fan, medical equipment. Leave out things you can live without for a few days.

Step 2: find each item's watts

Check the nameplate on each appliance or its manual. Note two figures where they exist: running watts (continuous) and starting watts (the brief surge motors draw when they start, which can be several times higher). If only amps are listed, watts ≈ volts × amps.

Step 3: add them up

• Add the running watts of everything that may run at once.
• Add the single largest starting surge on top (motors rarely start at the same moment).
• Leave a margin so the generator is not running at its limit.

Step 4: decide how it connects

Extension cords to individual appliances work for a portable unit. Powering house circuits requires a transfer switch or interlock installed by a licensed electrician — never plug a generator into a wall outlet.

Special cases

• Central air and well pumps have large starting surges; give providers the nameplate data.
• Medical devices may need clean (inverter) power; check with the device maker.

For kW and kVA terms used on larger units, see our sizing guide, and read generator CO safety before running any unit.