A refrigerator setting is not a temperature reading. To check whether the space holding your food is cold enough, use a thermometer. The FDA advises keeping the refrigerator at 40°F (4°C) or below and the freezer at 0°F (−18°C) or below. A number on the control dial alone cannot show what is happening on a shelf.
Where should the thermometer go?
For a useful check, put an appliance thermometer on a middle shelf and give the reading time to settle. Avoid judging the entire refrigerator by a brief reading at the open door. The USDA also describes a more specific test: put a suitable thermometer in a glass of water in the middle of the refrigerator and leave it for 5–8 hours. Follow your thermometer maker’s instructions before immersing a probe or display in water.
If the water reads outside the USDA’s suggested 38–40°F range, adjust the control and repeat the 5–8-hour check. This is a way to make a setting change and verify its result; it is not a reason to keep food at a warmer temperature while waiting. Keep perishable food at 40°F (4°C) or below.
| What you are checking | Where to measure | What to look for |
|---|---|---|
| Routine refrigerator monitoring | Appliance thermometer on a middle shelf | 40°F (4°C) or below |
| USDA water-glass setting check | Thermometer in a glass of water, middle of the refrigerator | Wait 5–8 hours; adjust if outside 38–40°F, then recheck |
| Freezer monitoring | Appliance thermometer in the freezer | 0°F (−18°C) or below |
What if the reading is too warm?
- Check the door first. Make sure it closes completely and nothing blocks the gasket.
- Adjust the temperature control according to the appliance manual. Do not assume a higher dial number means colder; controls differ.
- Measure again after 5–8 hours. The appliance needs time to respond to a setting change.
- If it remains above 40°F, investigate promptly. Do not use an unsafe reading as the normal storage condition for perishable food. Check the appliance instructions or arrange a repair.
A thermometer is particularly useful during a power outage because it gives you more than a guess about the temperature when electricity returns. The length of the outage and the type of food still matter; refrigerator and freezer decisions still require different checks.
Keep a short record
Note the shelf, whether you used a water glass, the start and end time, the reading and any control change. For example, a single 41°F (5°C) reading does not reveal how long food has been warm. Measure again after an adjustment and consider the food’s history before deciding whether it is safe. USDA’s freezer check is different from the water-glass method: place the thermometer between frozen-food packages and read it after 5–8 hours.
Common questions
Can I just trust the digital display?
The display may show a setting or a reading at a sensor rather than the temperature where your food is stored. A separate appliance thermometer checks the actual space. If the readings disagree, use the appliance instructions and repeat a settled measurement.
Should I use a meat thermometer to monitor the fridge?
A food thermometer is designed to measure an item when you insert its probe. An appliance thermometer is designed to remain in a refrigerator or freezer. For the water-glass test, use an instrument whose maker allows that use.
Once you have checked the refrigerator, you can apply the measured temperature to our hard-boiled egg storage guide.
Sources
- USDA FSIS, Appliance Thermometers — water-glass placement, 5–8-hour check and adjustment.
- FDA, Refrigerator Thermometers — refrigerator and freezer temperature targets.
Reviewed 28 September 2026. Food-safety guidance applies to ordinary household storage; follow your appliance and thermometer instructions.