Power station runtime calculator
Quick answer: usable watt-hours are the rated watt-hours times the station’s efficiency, and hours of runtime are usable watt-hours divided by the watts an item draws. A 1,000 Wh station at 85% has 850 Wh to use: about 94 hours for a 9-watt LED bulb, or about 34 minutes for a 1,500-watt space heater. (National Laboratory of the Rockies (U.S. Department of Energy); U.S. Department of Energy; Federal Trade Commission; National Renewable Energy Laboratory)
Runtime on a 1,000 Wh station
Usable energy: 1,000 Wh × 85% = 850 Wh.
Everything checked draws 41.5 W together, so running it all at once lasts about 850 Wh ÷ 41.5 W = 20.5 hours.
| Item: watts × how many | Alone | Wh a day |
|---|---|---|
| Refrigerator: 41.5 W × 1, 24 h a day (U.S. Department of Energy (FEMP); U.S. Department of Energy) | 20.5 h | 996 Wh |
| All items, per day | 996 Wh |
Days on one charge
At the hours you set, the items use 996 Wh a day, so one full charge covers 850 ÷ 996 = 0.9 days.
Station size for 3 days
Without recharging: 996 Wh × 3 ÷ 85% = 3,516 Wh of rated capacity.
Fit checks
- Refrigerator: compare any starting watts on its label or in its manual with the station’s surge rating.
- Charge the station on a solid, flat surface out of direct sunlight, with the charger that came with it. (U.S. Fire Administration (FEMA))
For a whole outage plan with water, food, and a checklist, use the power outage planner. For stored water and food, use the food and water calculator.
How the numbers work
- Daily energy is watts times hours used per day, the method the Department of Energy gives. The watts on a label are the most an appliance draws. (U.S. Department of Energy)
- A station loses some energy turning its battery into household power. No government source gives a figure for portable power stations, so the site starts at the 85% round-trip efficiency a Department of Energy lab uses for home batteries. Your station’s manual may list its own number; change it on the form. (National Laboratory of the Rockies (U.S. Department of Energy))
- Refrigerators and freezers cycle on and off, so their yearly energy is spread over every hour, as in the outage planner: 363.5 kWh a year for an efficient refrigerator and 395 kWh for an upright freezer. (U.S. Department of Energy (FEMP); ENERGY STAR (U.S. EPA and DOE)) While running they draw more than that average, up to the label watts, so check the label against the inverter too. (U.S. Department of Energy)
- Phone charging uses 3.5 kWh a year per charger and a modem 52.6 kWh, both spread over every hour. (National Renewable Energy Laboratory (for the U.S. Department of Energy)) A space heater draws 1,500 W. (National Renewable Energy Laboratory) A 12,000 Btu window air conditioner draws about 816 W while it runs. (U.S. Department of Energy (FEMP)) A 54.5-inch LED TV draws about 92 W over 5 hours a day. (U.S. Department of Energy (FEMP)) An LED bulb as bright as an old 60-watt bulb uses about 9 W. (Federal Trade Commission)
- Medical device watts come from published maker specifications for one common model each, the same figures the power outage planner uses. (ResMed (device maker); Philips Respironics (device maker); Pride Mobility (device maker)) Your own device may differ.
- None of the sources checked gives a starting-watts figure for a refrigerator, freezer, air conditioner, or heater, so the page asks you to compare the label with the station’s surge rating.
- Hours of daily use for the heater, air conditioner, and lights are the site’s starting choices. Change them to match your home.
Every source, the exact rule it supports, and the date it was checked are on the sources page.