What Size Portable Power Station Do You Need for Home Backup?
Short answer: add up the watt-hours your devices will use during an outage, add roughly 25–30% for conversion losses and headroom, and pick a power station with at least that much capacity. Then check two more numbers: its continuous output (watts) must cover everything running at once, and its surge rating must cover anything with a motor or compressor starting up. The calculator below does the math.
The three numbers on every power station
| Spec | Unit | What it tells you |
|---|---|---|
| Capacity | watt-hours (Wh) or kWh | How long it can run your devices. 1,000 Wh can supply 100 W for about 10 hours, before losses. |
| Continuous output | watts (W) | How much it can run at the same time. Add up the watts of everything plugged in at once. |
| Surge / peak output | watts (W) | A short burst for start-up. Fridges, freezers, pumps and some power tools pull several times their running watts for a moment when the motor starts. |
A big battery with a small inverter can run a fridge for a long time but can’t start a microwave. A big inverter with a small battery can start almost anything but runs out fast. You need both numbers to fit.
Step by step: size it yourself
- List what must stay on. Be strict: a short list is the difference between a portable unit and a whole-home system. Typical must-haves are the fridge, Wi-Fi router, phones, a few lights, a fan, and any medical device.
- Find each device’s watts. Look on the label or power brick (volts × amps = watts if only those are listed). For the fridge, don’t use the label’s watts × 24: compressors cycle on and off. A plug-in energy meter left on it for 24 hours gives you the real daily watt-hours.
- Multiply watts × hours you need each device per day to get watt-hours, then add them up.
- Divide by about 0.85. Turning battery power into household AC loses energy in the inverter, so you get noticeably less than the rated capacity from the AC outlets. Planning on roughly 80–85% usable is a common rule of thumb; check the maker’s own figure if it gives one.
- Multiply by the number of days you want to cover without recharging, or plan to recharge from solar during the day.
- Check output: the continuous watt rating should be above the total of everything you’ll run at the same moment, and the surge rating above the biggest motor’s start-up draw.
Power station calculator
Enter each device’s watts and how many hours a day it runs. For a fridge, enter its measured daily watt-hours as watts with 1 hour. Estimates only: your devices’ labels and the station’s own specs are what count.
| Device | Watts | Hours/day |
|---|---|---|
Days without recharging:
Your devices use about – Wh per day.
Suggested minimum capacity: – Wh (after ~15% inverter loss and 10% headroom).
A worked example
With the starting numbers in the calculator (example values, not measurements of any particular device): router 15 W × 24 h = 360 Wh, four 9 W LED bulbs for 5 hours = 180 Wh, phones and a laptop 60 W × 3 h = 180 Wh, and a fridge measured at 1,000 Wh a day. That’s 1,720 Wh a day. Divide by 0.85 and add 10% headroom and you get about 2,230 Wh (the calculator rounds up to 2,300). A station of roughly 2,000–2,500 Wh would cover one day; for two days, double it or plan to recharge.
Rough size classes
| Capacity | Typical use in an outage |
|---|---|
| Under ~700 Wh | Phones, laptops, Wi-Fi router, lights and a fan for an evening or a night |
| ~1,000–2,000 Wh | The above plus a fridge for roughly a day, depending on the fridge |
| ~2,000–4,000 Wh | A fridge, essentials and some cooking (a microwave or kettle in short bursts, if the output rating allows) for a day or more |
| Expandable systems, 5,000 Wh and up | Several home circuits through a transfer switch or home panel, multi-day outages, often paired with solar |
Every home is different: treat these as ballpark classes and size from your own list.
Big loads: what usually needs a larger system
- 240-volt appliances (well pumps, central air, electric ranges and dryers, many water heaters) need a system with 240 V output, or a dedicated home backup setup.
- Heat: space heaters and electric heat use a lot of energy per hour and drain a portable station quickly.
- Connecting to your home’s circuits (instead of plugging devices in) needs a transfer switch or a compatible home panel installed by a licensed electrician.
Recharging matters as much as capacity
Recharge time is roughly capacity ÷ charging watts, plus some loss. A 2,000 Wh station on a 1,000 W wall charger needs a bit over 2 hours; on 400 W of solar in good sun it needs more than 5 hours, and real-world solar output is usually below the panel’s rating. If you expect multi-day outages, look at the station’s maximum solar input and plan the panels to match.
Why a battery instead of a fuel generator?
A battery power station runs silently and has no exhaust, so it can be used inside (follow the maker’s instructions on ventilation and placement). A fuel generator can power more for longer if you have fuel, but it must run outdoors: ready.gov advises using generators only outdoors and at least 20 feet from windows, doors and attached garages, to prevent carbon monoxide poisoning. Some households use both.
How long you actually need to cover
Ready.gov notes that a closed refrigerator keeps food cold for about four hours and a full freezer holds its temperature for about 48 hours. If you just want to protect food through a short outage, you may need less capacity than you think. For medical devices, ask the device maker or your doctor how much backup time you need.
Source: ready.gov, “Power Outages” (read October 16, 2026).
Checklist before you buy
- Daily watt-hours from your own list (calculator above)
- Continuous output above everything you’ll run at once
- Surge rating that covers your fridge or pump starting
- 120 V only, or 240 V for well pumps and big appliances
- Expandable with extra batteries if your needs may grow
- AC charging speed and maximum solar input
- Outlets you need: AC, USB-C wattage, a car/RV port
- Weight and wheels, if you’ll move it around
Shop by size on Amazon
Compare capacity (Wh), output (W) and solar input on each listing.
Keep reading
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