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How Many Watt-Hours Do You Actually Need to Survive a Power Outage?

Skip the marketing capacity war. Here's the actual math for sizing a power station to what you're trying to keep running — not the biggest number you can afford.

7 min read·Gridalyn team

A watt-hour (Wh) is just a rate multiplied by time: a 100-watt device running for one hour uses 100Wh. Every runtime question reduces to that one formula. The part people skip is actually listing what they'd run and for how long — so we did it for you, three ways.

What common devices actually draw

"Running watts" is what a device pulls once it's on — ignore the surge/startup number on the box, it only matters for sizing a unit's peak output, not its capacity.

Device
Running watts
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Fridge and pump figures are average draw over a cycle, not the startup surge — a fridge compressor can spike to 3-6x its running watts for a second on startup.

Three real scenarios, worked out

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The short version

List what you'd actually run and for how long, multiply watts by hours, then buy 20-30% above that number for battery aging and inverter loss. Most homeowners overshoot capacity and undershoot planning.

See units sized for these scenarios →