How Long Will a Fridge and Freezer Stay Cold During a Power Cut?
Last reviewed: 20 August 2026
Quick answer: The Food Standards Agency says a fridge should stay cold for up to around 4 hours during a power cut if the door is kept closed. A full freezer can keep food frozen for up to around 48 hours, while a half-full freezer may manage around 24 hours. These are estimates, not guarantees.
Actual performance depends on the appliance, room temperature, how full it is and how often the door is opened. The simplest action is also one of the most effective: leave the doors shut.
The simple 4 / 24 / 48 rule
- Fridge: approximately 4 hours.
- Half-full freezer: approximately 24 hours.
- Full freezer: approximately 48 hours.
Use those numbers as planning estimates. The Food Standards Agency specifically notes that fridge and freezer temperatures vary by make, model, room temperature and how frequently the doors are opened.
Why does a freezer last longer than a fridge?
A freezer contains a large mass of already frozen food and operates at a much lower temperature. That stored cold energy slows the rate at which the contents warm after electricity is lost.
A full freezer generally performs better than a half-empty one because frozen food itself acts as thermal mass. Empty space contains air, and warm room air enters whenever the door opens.
What should you do immediately when the power goes off?
- Keep the fridge and freezer doors closed.
- Note roughly when the outage started.
- Check whether the outage affects the wider area.
- Avoid repeatedly opening the door to inspect the food.
- If you have a fridge/freezer thermometer, use it to monitor temperature.
- If the outage becomes prolonged, check current Food Standards Agency guidance.
If you are preparing for outages more generally, our 72-Hour Emergency Kit Checklist covers lighting, water, communications and food as well.
What temperature should a fridge be?
Under normal conditions, the Food Standards Agency recommends keeping a fridge at 5°C or below. During a power cut, its current advice says food can be stored at temperatures under 8°C.
If the temperature rises to 8°C or above, the FSA advises eating food that normally requires refrigeration within four hours first. This is where a simple appliance thermometer becomes particularly useful: it replaces guesswork with an actual temperature.
Should you move food outside in winter?
The Food Standards Agency says that when the weather is below 8°C, food can potentially be stored outside in clean, dry conditions, out of direct sunlight and protected from animals. It recommends using a sealed box to reduce contamination and tampering.
This is situational advice, not a reason to put food directly on a patio or in an insecure location. Outdoor temperatures can fluctuate and direct sunlight can warm a container even on a cold day.
Should you put ice packs in the fridge?
If you already have frozen gel packs or frozen water containers, they may help maintain a lower temperature when moved into the fridge. Do this strategically rather than repeatedly opening the freezer.
A cool box can also be useful for a small number of high-priority chilled items, particularly if you can maintain a safe temperature with frozen packs.
Can a portable power station keep a fridge running?
Yes, if the power station has enough battery capacity and sufficient inverter output and surge capacity for the fridge compressor.
Do not size a battery only from the fridge’s nameplate wattage. Refrigerators cycle on and off and their compressors can draw a short burst of extra power when they start.
Our portable power station sizing guide explains the basics, and our home-backup power station guide explains what to compare when buying.
How much battery capacity does a fridge need?
The most accurate approach is to measure the appliance’s energy use over a full day with an appropriate energy monitor. A refrigerator that averages 40–60W over time can consume far less energy than its maximum instantaneous draw suggests because the compressor is not running continuously.
As a rough example only, if a power station offers around 850Wh of usable energy and the refrigerator averages 50W, the theoretical runtime is around 17 hours. Real runtime will vary because of inverter losses, compressor cycling, ambient temperature and appliance efficiency.
Should you run a kettle or heater from the same battery?
Usually not if preserving refrigeration is the priority. A UK kettle may draw 2,000–3,000W and can consume a meaningful amount of battery energy in only a few minutes. Electric heaters are similarly demanding.
During a prolonged outage, use stored battery energy for the loads that deliver the greatest resilience per watt-hour: refrigeration, communications, essential lighting and critical equipment.
What food should you eat first?
If the outage lasts beyond the safe chilled-storage window, prioritise perishable refrigerated foods according to current Food Standards Agency guidance. Shelf-stable tins and cupboard food remain useful later because they do not depend on refrigeration.
Do not use smell or taste as the only test of safety. Harmful bacteria may not create obvious visible or sensory changes.
Can you refreeze food after a power cut?
This depends on whether the food remained safely frozen or how far it thawed and warmed. There is no single rule that applies to every food. If items have started to thaw during a prolonged outage, follow current FSA guidance for the specific food and temperature conditions.
If in doubt about high-risk food, safety is more important than avoiding waste.
Useful items to keep ready
- A fridge/freezer thermometer.
- Reusable freezer blocks.
- A cool box.
- A torch or head torch.
- A charged phone power bank.
- A modest supply of food that does not require cooking.
- A suitable portable power station if refrigeration is a household priority.
Frequently asked questions
Will milk be safe after a four-hour power cut?
Time alone is not enough to decide. The important factor is the temperature the milk reached. Follow the Food Standards Agency’s current chilled-food advice, especially if the fridge rose to 8°C or above.
Does a freezer stay colder if it is full?
Generally yes. The FSA’s planning estimate is around 48 hours for a full freezer compared with around 24 hours for a half-full freezer, assuming the door remains closed.
Should I open the freezer to check?
Avoid unnecessary opening. Every time the door opens, warmer air enters and reduces the remaining cold reserve.
Is a fridge thermometer worth buying?
For power-cut preparedness it is one of the cheapest useful tools because it tells you what the internal temperature actually is rather than forcing you to guess from elapsed time.
Bottom line
Remember 4 / 24 / 48: roughly four hours for a closed fridge, 24 hours for a half-full freezer and 48 hours for a full freezer. Keep the doors closed, use a thermometer where possible and follow Food Standards Agency guidance when an outage is prolonged.
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