The short answer
A full freezer keeps food frozen for about 48 hours if you leave the door shut, and a half-full one for about 24 hours. The USDA, the UK Food Standards Agency and the American Red Cross all give those two numbers. Australia's food regulator is more cautious and says a freezer shouldn't defrost for around 24 hours. Treat every figure as an estimate for a closed freezer, and check food by its temperature, not the clock.
Food safety is reference material here, not professional advice. For illness after eating suspect food, contact a doctor or your local emergency number.
The numbers, source by source
Here is what each official source says, read from the pages themselves.
| Source | Full freezer | Half-full freezer | Notes |
|---|---|---|---|
| USDA (US) | approximately 48 hours | 24 hours | Door closed |
| UK Food Standards Agency | up to 48 hours | 24 hours | "these are estimates" |
| American Red Cross | about 48 hours | 24 hours | Door remains closed |
| Food Standards Australia New Zealand | around 24 hours | not stated | Says "shouldn't defrost" |
The FSA adds that temperatures vary with the make and model of the appliance. That matters more than the table suggests: a new, well-sealed, well-stocked freezer and an old one with a worn door seal are different machines.
Upright or chest freezer?
None of the sources above gives a separate figure for chest and upright freezers, so we won't invent one. What they do say is that food in the front, in the door, or in small, thin packages will defrost faster than large, thick items or food in the back or bottom of the unit.
That is the USDA's wording about position, and it points at why people often report chests holding cold longer: lifting the lid of a chest is not the same as swinging open the door of an upright. That is our reading, not an official finding. Whichever you own, the advice is the same: keep it shut.
What makes a freezer last longer
Fullness is the biggest lever. The USDA tells you to keep the freezer full and to fill empty spaces with frozen plastic jugs of water, bags of ice, or gel packs. It also says to group foods together, which helps foods stay cold longer. If you can plan ahead, do this before storm season, not after the lights go out. Our power outage checklist has a place for it.
Keep the doors closed. The FSANZ phrase is "as much as possible", and that is a fair way to put it, since you will want to look.
For a long outage, the USDA says fifty pounds of dry ice should hold an 18-cubic-foot freezer for 2 days. The same page warns not to touch dry ice with bare hands or place it in direct contact with food. A thermometer in the freezer, as the Red Cross suggests, tells you the real state of things.
How long is the clock running?
Count from the moment the power went off, and use our power outage food timer to see how long the fridge and freezer have left. The FSA says an outage of less than 4 hours is unlikely to impact the safety of food in chilled or frozen storage. Eat what is in the fridge first, and since the FSA lists defrosted frozen food that doesn't need cooking next in its order of use, thawed items go early on the menu.
Refreeze or throw away?
The USDA's rule centres on ice crystals. Frozen foods that have thawed but still contain ice crystals may be safely refrozen, although quality may suffer. Food that stayed cold enough is on the same list.
Not everyone agrees. Australia's regulator says that if frozen foods have thawed, don't refreeze. The USDA allows it for food that still has ice crystals, and the Australian page gives a blunter rule. If you are unsure which applies, follow the stricter one and cook the food instead of refreezing it.
For anything else, the Red Cross says to throw out food that has been warmer than 40 degrees F. The USDA is just as blunt: never taste food to determine its safety.
Common questions
How long will a full freezer stay frozen without power?
About 48 hours with the door closed, per the USDA, the FSA and the Red Cross. The FSA calls these estimates, and Australia's regulator gives around 24 hours.
How long does a half-full freezer last in a power cut?
About 24 hours. Fill the gaps with frozen jugs of water or bags of ice to help it hold longer.
Does a chest freezer last longer than an upright?
No source we checked gives separate numbers. The USDA notes that food near the door and the front defrosts faster, which fits the common view that chests keep cold better, but that part is our reading.
Can I refreeze food that has thawed?
The USDA says food that still has ice crystals may be safely refrozen, though quality may suffer. Australian advice says not to refreeze thawed food, so when in doubt, cook it.
Is it safe to taste food to check?
No. The USDA says never to taste food to determine its safety.