What size generator do I need?

A generator is useful only when it can support the equipment you actually plan to run. Make a short list of essentials and use the wattage labels or manuals for those exact appliances. Avoid sizing from a generic “whole house” estimate when your real plan is to power only a refrigerator, lights, internet equipment, a furnace blower, or a sump pump.

Separate must-haves from nice-to-haves. During an outage you can often reduce the required generator size by staggering high-draw appliances instead of using them all at once.

Running watts are the steady power a device needs after it is operating. Starting or surge watts are the brief additional demand created when a motor or compressor starts. Refrigerators, pumps, air conditioners, and some power tools can have a much higher starting demand than their normal running load.

For a practical estimate, total the running watts for everything used simultaneously. Then add the largest difference between one device’s starting and running watts. Motors normally do not all start at the exact same instant, so adding every surge can oversize the plan.

• Total simultaneous running load
• Plus the largest additional startup surge
• Plus 15–25% capacity headroom

Suppose your essential load includes a 180-watt refrigerator, a 600-watt furnace blower, 60 watts of lighting, a 20-watt router, and 40 watts of phone charging. The continuous total is about 900 watts. If the refrigerator creates the largest extra startup demand—about 1,020 watts above its running load—the estimated peak becomes roughly 1,920 watts.

Adding 20% headroom produces a target near 2,300 watts. Rounding up to the next practical size class gives room for normal variation, aging equipment, and small additions. Always verify the nameplate and manual numbers before buying.

Wattage tells you whether a generator can start and operate the load. It does not tell you how long it will run. Engine-generator runtime depends on fuel tank size and load. Battery-station runtime depends on usable watt-hours, inverter efficiency, and the average load.

A simple battery estimate is usable watt-hours divided by average running watts. A 2,048Wh battery with 85% usable efficiency supplies about 1,740Wh, or roughly 1.9 hours at a 900-watt continuous load. Cycling appliances may extend real runtime, while cold weather and conversion losses may reduce it.

A portable generator feeding individual extension cords is different from equipment connected to household wiring. Whole-home connections, transfer equipment, grounding, fuel plumbing, and service-panel work should be evaluated by a qualified electrician or other licensed professional as required locally.

Never connect a portable generator to a wall outlet. This dangerous practice can energize utility lines and expose workers and neighbors to lethal voltage.