How to Calculate Fridge Runtime

Calculate fridge runtime from the refrigerator’s running power, cycling behavior, and usable battery energy. Battery capacity alone is not enough.

Find the appliance load

Use the refrigerator label, manual, or a suitable energy meter. Running watts can differ from startup demand, and the compressor does not normally run continuously.

For an estimate:

average refrigerator load =
running watts × duty cycle

Duty cycle changes with room temperature, food temperature, thermostat setting, door openings, ventilation, and appliance condition.

Calculate usable battery energy

For an AC-powered refrigerator:

usable energy =
rated battery capacity × inverter efficiency × available battery percentage

Then divide usable energy by the estimated average load.

The result remains an estimate. A planning margin is appropriate because inverter standby use and compressor cycling are difficult to predict precisely.

Check compressor startup

The power station must support both:

• The refrigerator’s running power
• The brief startup demand when the compressor begins operating

Do not assume a published surge number guarantees compatibility. Surge duration, waveform, protection behavior, and the appliance itself can affect startup.

Reduce energy use during an outage

• Keep the doors closed
• Let warm food cool safely before placing it inside
• Keep ventilation openings clear
• Avoid unnecessary ice making or rapid-cooling modes
• Place the power station where its ventilation remains unobstructed

The U.S. Food and Drug Administration states that an unopened refrigerator keeps food cold for about four hours during an outage. Food safety decisions should follow current FDA guidance rather than a runtime estimate alone.

Open the fridge runtime calculator

Open the fridge runtime calculator with an example refrigerator scenario, then replace every input with information from your appliance and battery.