Power station runtime calculator
Choose what you want to keep running and see how long your power station lasts, plus whether it can start everything at once.
Estimate your runtime
Add an appliance
How the calculator works
Runtime comes from three numbers: how much energy the battery stores, how much of it reaches your appliances, and how much those appliances use over a day.
The calculator takes the capacity you enter and multiplies it by 0.85. That covers the energy lost when the inverter converts battery power to 120 V household power. It then adds up each appliance's running watts, weighted by the hours per day it actually draws power, and divides.
The hours-per-day column matters more than people expect. A refrigerator is rated around 150 W, but its compressor cycles on and off, so over a day it averages far less. A CPAP runs only while you sleep. Change these hours to match how you would really use each device during an outage.
Output and surge: the two limits
Capacity is only half the story. Every power station has a continuous output limit in watts. If the appliances running at the same moment add up to more than that, the unit shuts off.
Anything with a motor or compressor (fridges, freezers, pumps, AC units) also pulls a short spike when it starts, often two to three times its running watts. That spike has to fit under the surge rating. The calculator checks both limits using the worst case: everything running, plus the biggest motor starting.
Want exact numbers? A plug-in watt meter costs about the same as a takeout dinner and shows what your appliance actually draws, including over a full day.
Real-world adjustments
- Cold weather reduces how much energy a lithium battery delivers. If it is stored in a cold garage, expect less.
- Older batteries hold less. After several hundred cycles, capacity drops noticeably, even on LiFePO4 models.
- Many units reserve a few percent of the battery to protect it, so the display reaches 0% before the cells are truly empty.
Frequently asked questions
How do I calculate power station runtime?
Multiply the capacity in watt-hours by about 0.85 to account for inverter losses, then divide by the average watts your appliances draw. A 1,000 Wh unit running a 100 W load lasts about 8.5 hours.
Why does my power station run out faster than the math says?
Inverter losses, battery age, cold temperatures and appliances that draw more than their label average all reduce runtime. Many units also stop before the battery is fully empty to protect it.
What is the difference between watts and watt-hours?
Watts measure how much power something draws at a given moment. Watt-hours measure stored energy. Output in watts decides what you can run; capacity in watt-hours decides for how long.
Does running on DC instead of AC last longer?
Usually yes. Powering a device from the 12 V or USB ports skips the inverter, which avoids roughly 10 to 15 percent of conversion loss.
Sources and method
Runtime figures assume 85% of battery capacity reaches AC appliances and typical US appliance ratings. See exactly how we calculate. Found a mistake? Tell us and we will fix it.