Is your fridge cold enough? Check 40°F, not the dial.

A dial that says 4 or “Colder” is not a temperature. An inexpensive appliance thermometer and one overnight check tell you whether the fridge holds 40°F or below and the freezer sits near 0°F.

Our take: before you buy a new fridge, a smart sensor or a pile of ice packs, measure. Put an appliance thermometer in a glass of water in the middle of the fridge, wait 5 to 8 hours, and read it. Federal guidance wants 40°F or below in the fridge and 0°F in the freezer. If either is off, move the control one step and check again. [S1] [S3]

Two numbers that matter

Fridge40°F or below, aim 38–40°F

Freezer0°F, check reads 0–2°F

Original schematic, not a reading from any appliance. Targets from USDA FSIS, FDA and CDC guidance. [S1] [S4]

Take a real reading before you change anything

The numbers on a fridge control are usually positions, not degrees. LG’s support page, for example, describes some controls as positions between Cold and Coldest and others as Min to Max. The only way to know the actual temperature is to measure it. USDA, FDA and CDC all point to the same tool: an appliance thermometer, unless the fridge already has a built-in display. [S8] [S2] [S4]

Use a refrigerator/freezer thermometer. USDA FSIS says these are designed to be accurate at cold temperatures. Some have a long probe and look like food thermometers, so check that the label says refrigerator/freezer. [S1]
Fridge: put the thermometer in a glass of water and set it in the middle of the fridge. Wait 5 to 8 hours, ideally overnight with the door shut, then read it. [S1]
Freezer: place the thermometer between frozen food packages. Wait 5 to 8 hours, then read it. [S1]

FSIS says the whole fridge should hold 40°F or below, so any shelf is safe for any food. Door bins swing more than the main cabinet, which is why FSIS and FDA both say to keep eggs and other perishables on a shelf, not in the door. [S2] [S3]

A warm reading is a food question first. USDA FSIS says foods held above 40°F for more than 2 hours should not be eaten. If you find a warm fridge, decide what to keep with the federal outage chart, and never taste food to judge it. When in doubt, throw it out. [S2] [S7]

What did the thermometer say?

Highlight your reading

Choose a reading to highlight its guidance.

On target

Leave the control alone

A fridge reading of 38 to 40°F and a freezer reading of 0 to 2°F is the window USDA FSIS gives for this check. Nothing needs buying or adjusting. Leave the thermometer in place so a power cut or a failing unit shows up as a number, not a guess. [S1]

Warm fridge

One step colder, then measure again

Move the control one step colder using the manual’s direction for your model. LG says to change one increment at a time and wait 24 hours to stabilize. Before blaming the fridge, check the habits the federal pages call out: doors closed tightly, no more opening than necessary, and shelves not so crowded that air can’t circulate. [S8] [S2] [S3]

Warm freezer

Adjust, and treat a weak top freezer as short-term

FSIS asks for 0 to 2°F on this check and says to adjust the freezer control if it reads higher. If a refrigerator’s freezing compartment can’t hold zero, FSIS suggests using it for short-term storage and using a free-standing freezer at 0°F or below for long-term food. [S1] [S6]

After an outage

Read the thermometer before you sort food

FSIS says that when the power comes back, food is safe if the fridge is still at 40°F and the freezer is at 0°F or below. FoodSafety.gov adds that a closed fridge holds safe temperatures for up to 4 hours, a full freezer for about 48 hours and a half-full one for about 24. Frozen food with ice crystals, or at 40°F or below, may be refrozen. [S1] [S7]

These are federal and manufacturer guidance branches, not a lab test of your appliance.

Adjust one step, then check again

FSIS says an adjustment period is often needed after changing the temperature, and its own check repeats the 5 to 8 hour wait. LG says to wait a full 24 hours between changes. Waiting the longer of your manual’s time and the overnight reading stops you from swinging the dial back and forth. [S1] [S8]

Match the reading to the action
Reading	Useful action	Limit
Fridge 38–40°F	Leave it. Keep the thermometer inside.	FSIS’s window for this household check, not a calibration. [S1]
Fridge above 40°F	One step colder; check door seal, crowding and door openings; recheck after the wait.	Food above 40°F for more than 2 hours should not be eaten. [S2] [S3]
Freezer above 2°F	Adjust the freezer control; recheck after 5 to 8 hours.	Food kept constantly at 0°F stays safe; quality fades with time. [S1] [S6]
No change after adjusting	Check the manual’s troubleshooting, then contact the maker or a technician.	This guide doesn’t diagnose compressors, fans or sealed systems. [S8]

Federal food-safety and manufacturer guidance, not comparative product testing. Control layouts differ by model.

Storage times live in the chart, not the dial

FoodSafety.gov’s cold storage chart assumes a fridge at 40°F or below and a freezer at 0°F or below. Its freezer times are for quality only, because food stored continuously at 0°F or below can be kept indefinitely. Those times only mean something if the thermometer agrees. [S5] [S6]

Thermometer in water

Read after 5–8 hours

One step, then wait

Measure, adjust once, measure again. If the manual and a generic tip disagree, follow the manual.

What is worth buying?

If your fridge has no built-in temperature display, the first purchase is a refrigerator/freezer appliance thermometer, ideally one for each compartment. FDA calls appliance thermometers the best way of knowing these temperatures and says they are generally inexpensive. It is not a new fridge, a pile of ice packs, or a deodorizer for a fridge that is actually running warm. [S3] [S1]

Our recommendation is to measure before spending. That can save a wasted purchase, but it can’t tell you why a fridge won’t hold temperature, and it doesn’t replace the maker’s troubleshooting or a technician’s diagnosis.

Before you change the dial again

I used a thermometer made for fridges and freezers.I read the fridge from a glass of water on a middle shelf after 5 to 8 hours.I read the freezer between frozen packages after 5 to 8 hours.I moved the control only one step and waited before checking again.

Before you turn the dial again

What temperature should my fridge be?

40°F (4°C) or below, according to USDA FSIS, FDA and CDC. FSIS gives 38 to 40°F as the target window for the glass-of-water check. Some makers set a colder default; LG’s support page lists 37°F. [S1] [S3] [S8]

Is a higher number on the dial colder?

Not necessarily. The numbers are positions, not degrees, and control layouts vary by brand and model. Check the manual, then confirm with a thermometer. [S8]

Can I use my meat thermometer instead?

USDA FSIS describes refrigerator/freezer thermometers as specially designed for accuracy at cold temperatures, and says some look like food thermometers with a probe. Use one made for the job, and keep it in the appliance. [S1]

How long do I wait after changing the setting?

FSIS repeats its check after another 5 to 8 hours. LG says to wait 24 hours between changes. Follow your manual if it gives a time. [S1] [S8]

The power went out. Is my food safe?

Check the thermometer first. FSIS says food is safe if the fridge is still at 40°F and the freezer at 0°F or below. Otherwise use the FoodSafety.gov outage chart item by item, and never taste food to decide. [S1] [S7]

Sources

Primary USDA, FDA, CDC, FoodSafety.gov and manufacturer guidance, checked October 14, 2026. Recommendations here are editorial interpretation of that guidance; no hands-on results are claimed.