Power Station Sizing Guide
Watts, watt-hours, and how to work out what will actually run — with the arithmetic shown, so you can check it against any station rather than trusting a badge.
Two numbers, and people buy the wrong one
Every power station has two headline figures and they answer different questions.
Watts (W) is output. It decides what you can run at once. If a station is rated 1,800 W and your microwave draws 1,200 W, it will run — but it may not also run the kettle.
Watt-hours (Wh) is capacity. It decides how long. A bigger Wh number does not let you run a bigger appliance; it lets you run the same appliance for longer.
Buying for watts when your problem is duration is the most common and most expensive mistake in this category.
The arithmetic, in three steps
-
Step 1 — Add up the draw
List what must run at the same time and add their wattages. Appliance labels carry the figure. That total has to sit under the station's continuous output rating, not its surge rating.
-
Step 2 — Divide for runtime
Runtime in hours is roughly capacity in Wh divided by your total draw in W. A 1,000 Wh station running a 100 W load is about 10 hours on paper.
-
Step 3 — Take the derate
Then remove roughly 10 to 15 percent for inverter losses, more in cold weather. That paper 10 hours is realistically 8 to 9. Size so the honest number covers you, not the paper one.
The figure that catches people out: startup surge
Anything with a motor — a fridge compressor, a well pump, a furnace blower, a compressor in the garage — draws far more for the first fraction of a second than it does running. A fridge that runs at 150 W can ask for several times that on startup.
This is why a station can be comfortably rated for an appliance's running draw and still shut down when it kicks in. Check the appliance's startup or locked-rotor figure against the station's surge rating, and if the nameplate does not give one, ask an electrician rather than guessing.
Four tiers, by what they cover
-
Small — devices and lights
Browse portable stationsPhones, laptops, a router, LED lighting, a CPAP. No motors. This tier is about portability and quiet, and it is genuinely useful the other 360 days a year.
-
Medium — the fridge stays cold
Browse home backupThe first tier that meaningfully covers an outage. Enough surge headroom for a fridge compressor and enough capacity to get through a night without rationing.
-
Large — days, not hours
Browse solar panelsExpandable battery capacity and solar input, so it refills while the grid is still down. Buy expandability here even if you only start with one battery.
-
Whole-circuit — wired in
Portable vs whole-homeAt this point you are choosing circuits rather than appliances, and an electrician is part of the purchase. Different decision, covered separately.
Frequently asked questions
Why does my station shut off when the fridge starts?
Startup surge. The compressor asks for several times its running draw for a moment, and the inverter protects itself. You need surge headroom, not more capacity.
Does cold weather change the numbers?
Yes. Lithium cells deliver less usable capacity when cold, and many units restrict charging below freezing. If the station lives in an unheated garage, size with margin and check the operating range.
Can I run a space heater?
Briefly, and it will empty almost anything in this category fast. Resistive heating is the least efficient thing you can ask a battery to do. Plan for blankets and keeping the fridge cold instead.
How do these ship?
Lithium battery products travel ground only, never air. Larger units can move as freight, and we confirm method and cost before the order goes in.
Send us your list and we will do the arithmetic
What has to run, and for how long. We will size it against what we actually carry and tell you when a smaller one is enough.
