How long will a power station run my fridge?

By Dave, generator and controls engineer · Last reviewed October 31, 2026

Why the label beats the wattage sticker

A fridge's compressor doesn't run all the time. It switches on, cools, and switches off, so its average draw is much lower than the watts it pulls while running. Battery runtime depends on the average.

The yellow EnergyGuide label (on fridges sold in the U.S.) gives the estimated electricity use in kWh per year, measured with a standard lab test. Divide by the 8,760 hours in a year and you have the fridge's average draw in watts. If the label is gone, search the model number. The same figure is usually on the maker's spec sheet or in the ENERGY STAR product list.

Think of it like a car's fuel economy rating. The top speed doesn't tell you how far a tank will go, the miles per gallon does. The kWh per year is the fridge's miles per gallon.

Why you get less than the battery's rating

• Usable capacity: the station keeps some charge in reserve to protect the battery. We assume 90% of the rated Wh is usable.
• Inverter losses: turning the battery's DC into 120 V AC wastes some energy as heat. We assume 85% efficiency.
• Idle draw: the inverter uses some power just by being on, even when the fridge's compressor is off. Check the spec sheet, or test it: note the battery percentage before and after a few hours with nothing plugged in.

So a 1,000 Wh station gives a fridge about 765 Wh before idle draw.

A worked example

A fridge labeled 600 kWh per year:

If the station's inverter also draws 10 W at idle, the 1,000 Wh runtime drops from 11 hours to 9. To run this fridge for a full 24 hours, you'd want at least 2,170 Wh of rated capacity, before idle draw.

Treat the result as a best case

The label figure comes from a standard test. Real use in an outage can be higher or lower:

• Higher in a hot kitchen, with an old fridge or worn door seals, or after loading it with warm food.
• Lower if you keep the door shut. A closed, full fridge holds its cold for a while, and you won't be opening it much.

Plan on getting somewhat less than the table says, and check the battery percentage over the first few hours to see how your fridge actually does.

Make sure it can start the fridge

Runtime isn't the only check. The compressor needs a burst of power to start, so the station's surge rating has to cover the fridge's starting watts. Its continuous output has to cover the running watts. See running watts vs starting watts. Fridges with inverter compressors start gently and are much easier on a power station.

More than a fridge?

The calculator works out output, surge and watt-hours for a whole list of appliances and an outage length. Its fridge value is deliberately on the high side: it assumes the compressor runs a third of the time at a high typical running wattage. For a single fridge, the label method here is closer to real use.

Average draw from the label
  W = kWh per year × 1,000 ÷ 8,760
    = 600 × 1,000 ÷ 8,760
    = 68.5 → 69 W (rounded up)

Usable energy for the fridge
  Wh = rated Wh × usable fraction
       × inverter efficiency
     = 1,000 × 0.9 × 0.85
     = 765 Wh

Runtime
  hours = usable Wh ÷ average W
        = 765 ÷ 69
        = 11.1 → 11 hours
          (rounded down)

With 10 W of idle draw
  hours = 765 ÷ (69 + 10)
        = 9.7 → 9 hours

Capacity for 24 hours
  rated Wh = W × hours
    ÷ (usable fraction
       × inverter efficiency)
    = 69 × 24 ÷ (0.9 × 0.85)
    = 2,164.7 → 2,170 Wh

References

• U.S. Federal Trade Commission, Energy Labeling Rule, 16 CFR Part 305 (the yellow EnergyGuide label).
• U.S. Department of Energy, test procedure for refrigerators and freezers, 10 CFR Part 430, Subpart B, Appendix A (how the label's kWh per year is measured).
• IEC 62552, Household refrigerating appliances: Characteristics and test methods (the international energy test).
• ENERGY STAR certified refrigerators and freezers product data (U.S. EPA and DOE).

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