How Many Watt-Hours Do You Actually Need?
This is the most common question we get before someone buys a portable power station: what size do I actually need? Buy too small and it can not run what you need it to. Buy too big and you have paid for capacity you will never use. This power station calculator answers that question directly. Check off the appliances you want to run, adjust the wattage or hours if your device is different, and the calculator works out your daily watt-hour requirement, then matches it against real power stations so you know exactly what size to buy.
Whether you are asking what size power station do I need for a CPAP machine overnight, sizing a battery for a weekend of camping, or planning whole-home backup power for an outage, the math works the same way. This portable power station calculator also works as a general watt hour calculator, battery sizing calculator, or backup power calculator for solar and off-grid setups, not just for buying a specific product.
This is not a discount on the battery's rated capacity. It sizes you a bigger battery than your raw total, so daily use only draws down part of it, covering inverter conversion loss and keeping the battery healthier long term.
your recommended power stations.
Why We Add a Safety Buffer
The buffer is not a discount on what the battery is rated for. It is extra headroom on top of your calculated need. Two real reasons this matters: the inverter that converts the battery's stored DC power into the AC power your devices use is not 100% efficient, typically 85 to 95%, so you draw somewhat more from the battery than your devices actually receive. Running a battery down to empty every single day also shortens its usable lifespan over time, even with LiFePO4 chemistry, which handles deep discharge far better than older battery types. Sizing a battery bigger than your bare math keeps daily use comfortably inside its capacity instead of running it right to the edge.
FAQ
What size power station do I need?
Add up the watts of everything you want to run at once, multiply by the hours you will run each device, and total the watt-hours. Add roughly 20% for safety margin. That total tells you the minimum rated capacity to look for.
How many watt-hours does a refrigerator use per day?
A modern energy-efficient refrigerator typically averages around 1,200 to 1,600 watt-hours per day, though this varies by size and age. Older or larger units can use significantly more.
Is a bigger power station always better?
Not necessarily. A larger power station costs more, weighs more, and takes longer to fully recharge from solar. Sizing to your actual need, plus a safety buffer, is usually the better value than buying the largest available option.
Do I need to add a buffer to my watt-hour total?
Yes. Inverter conversion loss and battery longevity both mean a bare calculated total leaves no margin. A 15 to 25% buffer is a reasonable range for most households.
Can one power station run my whole home during an outage?
Larger expandable power stations can cover whole-home backup for essential circuits, but running an entire house including central air conditioning usually requires a much larger system or a traditional generator. This calculator is best suited for sizing essential circuits and specific appliances.