How do I know if a fridge is cold enough?

Almost nobody knows what temperature their fridge actually runs at, because the control is a number from one to five and the readout, if there is one, reports what it is aiming for rather than what it achieved.

Safety

Step by step

1. Get a fridge thermometer.They cost very little. Without one this is guesswork, and the dial tells you nothing about the actual temperature.
2. Measure in a glass of water.Stand the thermometer in a glass of water on the middle shelf and leave it overnight. Measuring air temperature gives a reading that swings every time the door opens; water shows the temperature the food is actually held at.
3. Aim for 0 to 5°C.The Food Standards Agency recommends below 5°C. Around 4°C is a sensible target that gives some margin without freezing things at the back.
4. Understand the dial.On most fridges the numbers are a power setting, not degrees — and higher usually means colder. Turning it to 5 does not mean 5°C.
5. Measure in more than one place.The back is coldest, the door is warmest, and the difference can be several degrees. Test the middle shelf and the door separately.
6. Store food by zone.Raw meat and fish on the bottom shelf so nothing drips onto other food. Dairy and cooked items in the middle. Salad in the drawer. Door for condiments and juice — never milk or eggs if you can avoid it.
7. Do not overfill it.Air has to circulate. A packed fridge has warm pockets and the thermometer only tells you about where it is standing.
8. Keep the vents clear.The cold air outlet at the back should not be blocked by a large container. It is a common cause of one shelf being warm while the rest is fine.
9. Check the door seal.Close it on a sheet of paper — if it slides out easily, the seal is not gripping. A failing seal makes the fridge run constantly and still not hold temperature.
10. Allow for a warm room.A fridge in a hot kitchen or a garage in summer works much harder. Most have a stated ambient range, and a garage in winter can be too cold for the thermostat to work properly.
11. Clean the condenser coils.At the back or underneath. Dust makes the fridge less efficient and it is a genuine cause of poor cooling. Unplug first.
12. Check the freezer at the same time.It should be at or below −18°C. The same principle applies: measure rather than trusting the dial.
13. Re-measure after any change.Adjusting the dial, moving the fridge, or a very full shop. Give it 24 hours to settle before reading.

Tips

• Thermometer in a glass of water, overnight, middle shelf. Air readings swing with every door opening.
• The dial is a power setting, not degrees. Higher usually means colder.
• Test the door as well as the middle. Several degrees difference is normal, which is why milk in the door is a bad idea.

Common mistakes

• Trusting the dial or the digital display — The dial is a power setting and built-in displays report the target rather than the achieved temperature. Only a thermometer in the fridge tells you the truth.
• Keeping milk and eggs in the door — The door is the warmest part and swings most with opening. High-risk items belong on a shelf.

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