Here’s something most people don’t find out until they’re standing in front of a thawed-out freezer full of ruined food: a full freezer will hold a safe temperature for about 48 hours after the power goes out. But if it’s only half full? That drops to 24 hours.
Why the difference? A full freezer is basically a giant block of cold mass. All that frozen food acts like insulation — the items keep each other cold. A half-empty freezer has a lot of air space, and air doesn’t hold cold nearly as well. So the emptier it is, the faster it warms up.
According to FoodSafety.gov, both of those time estimates — 48 hours and 24 hours — assume the door stays closed the whole time. That part matters more than most people realize. Every time you open the freezer, you’re letting cold air out and warm air in. Do that a few times and you’ve cut your safe window down significantly.
So the move during a power outage is simple: don’t open the freezer unless you absolutely have to. Seriously. Just leave it alone.
If the outage is going to last a long time and you want to protect a fully stocked freezer, the FDA notes that 50 pounds of dry ice should keep an 18 cubic foot freezer cold for roughly two days. That’s a solid backup plan if you know a storm is coming and you have time to prep.
When the power comes back on, the rule is: if the food still has ice crystals or feels refrigerator-cold (40°F or below), it’s generally safe. If it’s been above that temperature for more than two hours, the safer call is to throw it out. When in doubt, don’t eat it — foodborne illness is not worth the savings.