What Size Power Station Do I Need?

Tell us what you want to run and for how long. We work out the capacity (watt-hours) and the minimum output (watts) to look for — with an honest headroom margin, because buying one too small is the number-one thing owners say they regret.

What do you want to run?

Click a preset to add a typical wattage, then set how many hours per day you’ll run it. Adjust wattage to match your device’s label.

For how long?

Battery type of the station you’ll buy

Battery chemistry Affects how much of the rated capacity you actually get (95% vs 80%).

The size to look for

Aim for a power station of at least
—
Add a device to see your size.
Energy per day
— Wh
Energy for your days
— Wh
Min. rated capacity
— Wh
Min. output (all on)
— W

How the sizing works

Energy per day = each device’s watts × hours per day, added up.

Rated capacity needed = (energy per day × days) ÷ 0.8. The 0.8 accounts for usable depth-of-discharge (LiFePO4 ~95%, lithium-ion ~80%) and inverter conversion loss (~15% on AC). A station never gives you 100% of its label to your outlets.

Headroom: we then add ~20% because real loads run higher than planned, batteries age, and cold weather cuts capacity. Undersizing is the most common owner regret — a small buffer is cheap insurance.

Minimum output (watts) is the sum of everything running at once. The station’s continuous-output rating must clear this, and motors (fridge, pump, microwave) also have a brief startup surge — pick a pure sine wave unit with surge headroom for those.

Estimates only. Real needs vary with temperature, battery age, device duty cycles, and inverter quality. Check each device’s rating label for its actual wattage. We are not affiliated with any manufacturer mentioned on this page.

⚡ Power station size calculator — PowerStationTips

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Stations that match your size

The capacity above is one half of the answer; the other is whether the station’s continuous output clears your devices’ combined draw and startup surge. These tiers are a starting point — cross-check the specific model’s reviews before buying.

Compact tier · under 800 Wh

CPAP overnight, router + laptop for hours, phones and lights, a mini fridge for part of a day. Output ceiling ~700–1,200 W.

Mid tier · 800–2,000 Wh

A full-size fridge for 8–12 hours, CPAP + fridge overnight, comms and lights through a day-long outage. Output ceiling ~1,500–2,400 W. The most common single-outage size.

Large tier · 2,000 Wh and up

Fridge + medical device + comms for an overnight or multi-day outage, RV daily use, expandable battery base. Output ceiling ~2,000–3,600 W. Pair with solar to recharge between days.

Need multiple days or whole-home medical backup? An expandable large unit like the Anker SOLIX F3800 with solar is the configuration for sustained loads. We cover other models on the brand pages.

How to size a power station (without buying too big or too small)

The most common mistake is buying on the headline capacity number alone. A “1,000Wh” station does not deliver 1,000Wh to your devices — after battery derating and inverter losses you get roughly 800Wh, and real loads run higher than the neat numbers on a spec sheet. Owners who buy for the exact minimum are the ones who post “I wish I’d gone bigger” a month later. Size for your real load, then add a buffer.

Two numbers decide it, and you have to clear both:

  1. Capacity (watt-hours) — how long it runs. This is your total daily energy (watts × hours for every device) times the days you want to cover, divided by ~0.8 for losses.
  2. Continuous output (watts) — whether it can turn your devices on at all. Add up everything running at once; the station’s output rating must exceed that, with extra headroom for the startup surge of any motor (fridge, pump, microwave, well pump).

Common sizing questions

Is it better to buy a bigger power station than I need?

A moderate buffer, yes. Undersizing is the number-one regret in owner discussions — capacity fades as batteries age, cold weather steals usable Wh, and the load you actually plug in is always a little more than the load you planned. A 20% margin is cheap; running out overnight is not. Going wildly oversized only costs you money and weight, so aim for “comfortably above your real number,” not “the biggest one sold.”

How do I size for a refrigerator?

Use the fridge’s average draw, not its nameplate. A compressor rated at 150W only runs ~30–40% of each hour, so it averages about 50–60W — roughly 1–2kWh per day. Enter that average here, or use the refrigerator backup guide for the duty-cycle-corrected number.

Already have a station and want to know how long it lasts?

Use the reverse tool: the Power Station Runtime Calculator takes a capacity you already own and tells you how many hours it will run a given load.

Sizing calculator FAQ

What size power station do I need?
Add up each device’s watts multiplied by the hours per day you’ll run it to get watt-hours per day, multiply by the number of days you want to cover, then divide by about 0.8 to allow for inverter and battery losses. That gives the rated capacity (Wh) to look for. For example, a 60W CPAP for 8 hours plus a fridge averaging 55W for 24 hours is roughly 1,800Wh/day — so you’d want a 2,000Wh+ station for a single overnight outage. This calculator does that math for you.
Watts vs watt-hours — what’s the difference?
Watts (W) measure how much power a device draws at any instant — that sets the minimum inverter output your station needs. Watt-hours (Wh) measure energy over time (watts × hours) — that sets the battery capacity you need. A power station is rated in both: a continuous output in watts (can it turn the device on?) and a capacity in watt-hours (how long will it run?). You have to clear both numbers.
Should I size to the exact number or bigger?
Bigger, within reason. Buying too small is the single most common regret owners report — real loads are always higher than planned, batteries lose capacity as they age, and cold weather cuts usable capacity. We add a 20% headroom margin to the raw requirement for this reason. Undersizing by a little means you run out in the middle of the night; a modest buffer is cheap insurance.
Why divide by 0.8 for losses?
A power station never delivers 100% of its rated capacity to your AC devices. LiFePO4 chemistry gives you about 95% of nameplate; the inverter that converts DC to household AC costs another ~15%. Multiply those and you get roughly 0.8 — so a 1,000Wh station delivers about 800Wh to your outlets. Sizing has to account for that, which is why the required capacity is always higher than the raw watt-hours you need.