How to size a power station — the three numbers

Sizing a power station isn't one number, it's three: enough running watts, enough surge, and enough watt-hours. Miss any one and the unit either won't start your gear or won't last. Here's each in plain English — and the trick that stops you from overbuying.

1. Running watts — can it carry the load?

Add up the running watts of everything you'll have on at the same time. That total is your continuous load, and your power station's continuous (rated) output has to be at least that much. A fridge (~150 W) plus some lights (~100 W) plus a phone charger is well under 300 W; a space heater alone is 1,500 W. We sum the running watts of your selected appliances and compare to each unit's continuous rating.

2. Surge watts — can it start your motors?

Anything with a motor or compressor — a fridge, a sump pump, a well pump, an AC, a furnace blower — pulls a big surge the instant it starts, often 2–4× its running watts and lasting a fraction of a second. The worst case is the biggest single surge landing while everything else is already running, so that's exactly what we compute: max(surge of one device + running watts of the rest). Your unit's surge / peak rating has to clear that number. It's the reason a 1,000 W unit that easily runs a 800 W sump pump still can't start it — the pump surges to 1,500 W.

3. Watt-hours — how long will it last?

Watt-hours (Wh) are the size of the tank. The naïve formula is running watts × hours, but that's where most people overbuy by 2–3×, because fridges and pumps don't run constantly. A fridge compressor cycles on maybe a third of the time; a sump pump runs minutes per hour. So we use each load's duty cycle — the fraction of time it actually draws power — to get the true average draw, then:

That's why a 1,000–1,500 Wh unit keeps a fridge cold all day even though 150 W × 24 h looks like 3,600 Wh — the fridge only averages ~50 W.

4. Don't oversell — smallest sufficient first

Once we have the three requirements, we list the units that clear all three, smallest capacity first, and recommend that one — plus a meaningful step-up for headroom. Buying far more watt-hours than your load can use in the time you need is wasted money and weight. The only time we point you bigger is when no single battery holds enough energy (partial- and whole-home loads), where the honest answer is an expandable system you add batteries to.

Appliance wattages: standard appliance/generator sizing charts. Station specs: manufacturer published specifications (compiled 2026-06-15; approximate). See methodology & sources. Informational only — a computed sizing estimate from published appliance-wattage charts and manufacturer station specs. It is not an electrical guarantee. For hardwired or whole-home backup, transfer switches, or any permanent install, consult a licensed electrician.