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What size power station do I need?
List your devices and how many hours a day you run them to get the battery capacity (Wh), continuous output and surge rating your power station needs.
Results
| Minimum rated capacity | 3,265 Wh |
|---|---|
| Recommended capacity (+20% for aging and cold) | 3,918 Wh |
| Daily device energy (AC side) | 2,375 Wh/day |
| Continuous output needed (all on at once) | 187 W |
| Surge output needed | 1,327 W |
| Estimated solar contribution | 0 Wh/day |
About this calculator
Buying a power station by the advertised battery number is how people end up with a unit that dies at 3 a.m. Sizing works the other way around. Start from what you'll power and for how long, add the losses, then pick a battery big enough to cover it with some margin to spare.
This calculator turns a device list into the three specs that matter: capacity (Wh, how long it lasts), continuous output (W, how much it can power at once) and surge output (W, whether motors can start). You can also add solar to see how much panel input shrinks the battery you need.
How to use it
- Add each device with its wattage and the hours per day it actually runs. Fridges and freezers run 24 hours at their average draw.
- Set how many days you need to last without recharging. One day suits most outages. Use 2-3 days for storm-prone areas.
- If you'll recharge from solar, enter the panel watts and your peak sun hours (about 3-6 in most of the US).
- Pick a model whose rated Wh is at least the recommended figure and whose continuous and surge ratings exceed the output results.
The formula
Daily energy = Σ (watts × quantity × hours per day).
Battery energy per day = daily energy ÷ inverter efficiency + idle watts × hours the inverter is on.
Minimum capacity = (battery energy per day − solar energy per day) × days ÷ usable share.
Surge needed = total running watts + the largest single (starting − running) difference.
Worked example (default values)
Inputs
| Devices and daily hours of use | Refrigerator (full size, average draw): 60 W, 24 h/day; Wi-Fi router + modem: 15 W, 24 h/day; Laptop: 60 W, 4 h/day; LED light bulb: 9 W × 3, 5 h/day; CPAP (no humidifier): 25 W, 8 h/day |
|---|---|
| Days without recharging | 1 days |
| Usable share of rated capacity | 90 % |
| Inverter efficiency | 88 % |
| Inverter idle draw | 10 W |
| Hours per day the inverter is on | 24 h |
| Solar panel watts (optional) | 0 W |
| Peak sun hours per day | 4 h |
Results
| Minimum rated capacity | 3,265 Wh |
|---|---|
| Recommended capacity (+20% for aging and cold) | 3,918 Wh |
| Daily device energy (AC side) | 2,375 Wh/day |
| Continuous output needed (all on at once) | 187 W |
| Surge output needed | 1,327 W |
| Estimated solar contribution | 0 Wh/day |
Tips and common mistakes
Why add 20%? Lithium batteries lose capacity gradually, roughly 20% over their rated cycle life, and deliver less energy when they're cold. A station sized exactly to today's needs will come up short in a winter outage two years from now.
Capacity vs. output are separate decisions. Someone running a CPAP and a router for a week needs lots of Wh but only a small inverter. Someone who wants to run a microwave for ten minutes needs a big inverter but not much capacity. Expandable stations that take add-on batteries let you buy the output once and grow capacity later.
Frequently asked questions
What size power station do I need for a power outage?
To keep a fridge, router, phone charging and a few lights going for 24 hours, most homes need about 2,000-3,500 Wh of rated capacity and 1,000-1,800 W of output. Run your own list above, because one space heater or a well pump changes the answer completely.
Is 1000 Wh enough for camping?
For lights, phones, a fan and a 12 V cooler, yes, usually for 1-2 days. A 12 V compressor cooler averages roughly 15-30 W, which works out to about 400-700 Wh per day.
Do I need pure sine wave output?
Virtually all modern lithium power stations are pure sine wave. It matters for CPAPs, motors, chargers with sensitive electronics and some medical devices.
Can solar replace a bigger battery?
Partly. Solar only produces during the day and drops sharply when it's cloudy. Size the battery to cover at least your overnight use, and treat solar as a way to stretch multi-day outages.
Related calculators
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- Solar panel size calculator
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- Generator vs power station cost calculator
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Estimates for planning only, based on the assumptions shown. Real-world performance varies with equipment, temperature and installation. Updated October 19, 2026. See our methodology.