Understanding refrigerator backup sizing
Why this number is a conservative estimate
This calculator assumes the fridge runs continuously at its rated wattage, which overstates real energy use since compressors cycle on and off rather than running nonstop. In practice, most fridges only run their compressor roughly a third of the time, a duty cycle pattern reflected in ENERGY STAR's refrigerator energy use ratings, so actual daily energy use is often lower than the continuous-running math suggests. Treat this number as a safe upper bound rather than a precise prediction. The freezer backup tool uses the same conservative approach for a chest or upright freezer.
Why door opening habits matter during an outage
Every time the refrigerator door opens, warm air enters and the compressor has to work harder afterward to bring the interior back down to temperature. Minimizing door openings during an outage, and keeping frozen items like ice packs inside to absorb heat, both help stretch your actual battery runtime closer to the conservative estimate this calculator provides, consistent with FoodSafety.gov's power outage guidance.
Running watts versus startup surge
Battery capacity sizing cares about running watts, since that determines the total energy consumed over the backup period. Startup surge, when the compressor motor briefly draws several times its running wattage to start spinning, matters for inverter sizing instead. A battery can hold plenty of energy but still fail to start a fridge if the inverter can't handle that momentary surge. The battery inverter pairing tool covers this distinction, and the inverter continuous vs peak rating calculator in our Inverters & Equipment category breaks it down further.
When a portable power station is enough, and when it isn't
A portable power station in the 1 to 2 kWh range can typically run a standard refrigerator for 8 to 16 hours, which covers a short evening outage without needing a full home battery installation. For outages lasting multiple days, that same math requires either several portable units or a proper home battery system in the 10 to 15 kWh range. The 24 hour backup tool marks roughly where that crossover happens.
What to do with this number next
If you're backing up more than just the fridge, the critical loads calculator adds in lighting, internet, and other essentials together. If cost is the main concern, the cost per kWh comparison tool shows what different battery options run. If you're financing a small battery system around this and similar essential loads, the quick financing comparison tool in our Financing category gives a fast cost overview.