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Power station size calculator

Tick the devices you want to keep running in a power cut and how long for. We’ll tell you the battery size and power output to look for – and when a battery alone isn’t realistic.

What do you want to keep running?
  • all day
  • h/day
  • h/day
  • h/day
  • h/day
  • h/day
  • h/day
  • h/day
7 days

Free · No sign-up · Nothing you enter leaves your device · Updated November 2026

Your result

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How the calculator works

  1. For each device, we multiply its typical power use (watts) by the hours a day you’ll run it. Fridges switch on and off, so we use a daily figure instead.
  2. We add up the daily total and multiply by the number of days.
  3. We allow for the energy lost when a power station converts battery power to mains power.
  4. We pick the smallest size that covers that energy and can supply enough watts to run everything at once.

Worked example

Two phones, a Wi-Fi router and a laptop for 3 days:

  • Phones: 2 × 15 Wh = 30 Wh a day
  • Router: 12 W × 24 hours = 288 Wh a day
  • Laptop: 60 W × 3 hours = 180 Wh a day
  • Total: 498 Wh a day × 3 days = 1,494 Wh, or about 1,760 Wh of rated capacity after losses

So you’d look at power stations of around 2,000 Wh. Drop the router overnight and a 1,500 Wh model may do.

Choosing a power station

  • Capacity (Wh) – how long it lasts. Use the calculator above.
  • Continuous output (W) – must be higher than everything you’ll run at once.
  • Surge rating – fridges and freezers draw a short spike when the compressor starts. Check the surge (peak) figure.
  • Battery type – LiFePO4 (lithium iron phosphate) batteries generally last for more charge cycles than other lithium types.
  • Recharging – from the mains, a car socket or a solar panel. Check the solar input rating if you plan a longer outage.

Device figures are typical values. For the most accurate result, check the label on your own appliance – it usually shows watts, or annual kWh for fridges.

Frequently asked questions

What size power station do I need to run a fridge in a power cut?

A large fridge-freezer typically uses around 1,000 Wh or more a day, depending on its energy rating. To run one for a full day you need a power station of roughly 1,500 Wh or more, allowing for conversion losses. For several days, a battery alone becomes impractical, so most people pair a station with a solar panel or only run the fridge for part of the day.

What do Wh and W mean on a power station?

Watt-hours (Wh) is how much energy the battery holds – the size of the tank. Watts (W) is how much power it can deliver at once. You need enough Wh to last as long as you want, and enough W to run everything you switch on at the same time.

Why is the recommended size bigger than my total?

Power stations lose some energy converting battery power into mains (AC) power. We assume you can use about 85% of the rated capacity, so the rated size you need is a little higher than the energy your devices use.

Can a power station run an electric heater?

Only briefly. A heater on a low setting uses around 1,000 W, so even a 2,000 Wh station would run it for under two hours. Blankets, sleeping bags and warm layers are far more effective during a power cut.

Is it safe to use a power station indoors?

Battery power stations do not produce fumes, so unlike petrol generators they can be used indoors. Follow the manufacturer’s instructions on ventilation, charging and storage.

More calculators

General guidance only – not a substitute for official or medical advice. See every figure we use and where it comes from.