Maintenance procedure · Written to ASD-STE100 Issue 9 · Formatted to ANSI Z535

Check a Food or Fridge Thermometer Against a Known Temperature

For dial (bimetal) and digital probe, meat, and refrigerator/freezer thermometers — the ice-point test, the boiling-point test, and the calibration nut
ApplicabilityDial (bimetal) and digital contact food thermometers — probe, instant-read, meat, and oven-safe types — and dial or digital refrigerator/freezer (appliance) thermometers. This page does not cover infrared (non-contact) thermometers; see this site's page on checking an infrared thermometer for that instrument.
Task time24 min to 34 min editorial estimate, not a measurement
PersonnelOne
Revisionv1 · 2026-08-04
BEFORE YOU BEGIN

Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.

Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.

Summary

A food thermometer or a fridge or freezer thermometer is only useful if the number it shows is close to the truth. The most reliable way to find out is to test it against a fixed, known temperature rather than simply trust the dial or the display. The easiest fixed point to build in a kitchen is the ice point: a slurry of ice and water, which sits very close to 32°F (0°C). This page shows how to build that test, read it correctly, and adjust a dial thermometer's calibration nut or a digital thermometer's CAL function, on the models that have one.

This page will not tell you whether your specific thermometer has a calibration nut or a CAL button, because that is a decision each manufacturer makes model by model, and most digital thermometers have no way for a reader to adjust them at all. It also will not give you a certified calibration to a traceable standard — that is a laboratory service, not a kitchen check. What it gives you is an honest field test: whether your thermometer reads close enough to a known point to trust it, and what to do next if it does not.

Safety

NOTICE

THIS PAGE IS A FIELD TEST.
It is not a laboratory calibration. The ice-point test compares your reading with a known value. It does not give you a certified calibration. For a certified calibration, contact the manufacturer or a calibration laboratory.

WARNING

DO NOT USE A THERMOMETER FOR FOOD SAFETY WORK IF IT FAILS THIS CHECK.
Undercooked meat, poultry, or egg dishes can cause a severe illness.

Necessary equipment

ItemNote
Instructions for your own thermometerYour model decides whether it has a calibration nut or a CAL button.
Clean container for ice waterUse a tall glass or a cup deep enough for the stem.
Small wrench or pliers optionalUse this tool only if your dial thermometer has a hex nut under the dial.
Pot and a stove optionalUse this only for the boiling-point method.
Oven mitt or pot holder optionalUse this only for the boiling-point method.
Pen and paper, or a note appUse this to record each reading.
Ice materialUse ice cubes. Crushed ice also works.
Cold tap water materialUse this to make the ice slurry.

Specifications

Maximum adjustment your thermometer's calibration nut or CAL function allows
Unverified — do not rely on this value
CONSULT THE INSTRUCTIONS FOR YOUR OWN THERMOMETER, OR THE MANUFACTURER.

No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.

Start

Estimated 4 min to 6 min

NOTEThis check works for dial and digital thermometers with a metal stem. It does not cover infrared thermometers.
Whether your thermometer has a calibration nut or a CAL function
Unverified — do not rely on this value
CONSULT THE INSTRUCTIONS FOR YOUR OWN THERMOMETER.

No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.

  1. Read the instructions for your own thermometer before you start.
    • Find the word calibration or recalibration in the instructions.
    • Note whether your thermometer has a hex nut under the dial.
    • Note whether your thermometer has a CAL button or a reset function.
    2m
  2. Get a container for the stem of your thermometer.
    • The container must be deep enough to cover the stem.
    <1m
  3. Get some ice and cold water.
    • Also get a pen and paper to record your readings.
    1m
  4. If your dial thermometer has a hex nut, get a small wrench or pliers.
    <1m

The ice-point test

Estimated 4 min to 6 min

NOTEThe ice point is 32°F (0°C). Water freezes at this temperature at standard air pressure.
Ice point (the freezing point of water) reference temperature
Manufacturer or standard verified
32 °F

Source: SI Units – Temperature · tier 1 · accessed 2026-08-04

  1. Fill the container with three parts crushed ice to one part cold water.
    • Stir the ice and water together.
    • Let the mixture stand for three to five minutes.
    2m
NOTICE

KEEP THE DISPLAY AND THE BATTERY COMPARTMENT OF A DIGITAL THERMOMETER DRY.
Water inside the display can damage the electronics.

  1. Put the stem of the thermometer into the middle of the ice slurry.
    • Push a dial thermometer stem in at least three inches (7.6 cm).
    • Push a digital thermometer stem in at least two inches (5 cm).
    • Do not let the stem touch the bottom or the sides of the container.
    <1m
  2. Wait until the reading on the display or the dial becomes steady.
    1m
  3. Read the temperature while the stem stays in the ice slurry.
    • A correct reading is 32°F (0°C).
    • This kind of slurry is rarely exact.
    • Expect a value near 34°F (1°C).
    <1m
  4. Write down the reading and today's date.
    <1m
  5. Compare the reading with the ice point, 32°F (0°C).
    <1m

Adjust a dial thermometer

Estimated 3 min to 4 min

NOTENot every dial thermometer has a hex nut. Some dial thermometers have no adjustment.
  1. Stop this section if the reading is already 32°F (0°C).
    <1m
  2. Stop this section if your dial thermometer has no hex nut.
    <1m
  3. Hold the dial firmly with one hand.
    <1m
NOTICE

DO NOT FORCE THE HEX NUT.
A forced nut can break the movement inside the dial.

  1. While the stem stays in the ice slurry, turn the hex nut with the wrench or pliers.
    • Turn the nut clockwise to raise the reading.
    • Turn the nut counterclockwise to lower the reading.
    • Stop when the dial reads 32°F (0°C).
    1m
  2. Remove the thermometer from the ice slurry.
    <1m
  3. Put the stem back into the ice slurry to read the new value.
    1m

Reset a digital thermometer

Estimated 1 min

NOTENot every digital thermometer has a CAL button. Few digital thermometers have a reset function.
  1. Stop this section if the reading is already 32.0°F (0°C).
    <1m
  2. Stop this section if your digital thermometer has no CAL button or reset function.
    <1m
  3. If the ice slurry reads between 30°F and 34°F (-1°C to 1°C), hold the CAL button for two seconds.
    • The display goes blank for two seconds.
    • The display then shows 32.0°F (0°C).
    <1m
  4. Compare the new reading with 32°F (0°C).
    <1m

The boiling-point test

Estimated 11 min to 16 min

NOTEUse this method only if the scale on your thermometer reaches 212°F (100°C). Most fridge and freezer thermometers do not.
Boiling point of water at sea level, for the boiling-point check
Manufacturer or standard verified
212 °F

Source: How to Recalibrate Your Thermometer · tier 1 · accessed 2026-08-04

Boiling-point change per 500 feet (150 m) of elevation gain, per CDN's own instructions
Manufacturer or standard verified
0.5 °F

Source: How to Recalibrate Your Thermometer · tier 1 · accessed 2026-08-04

  1. Skip this section if your thermometer's scale does not reach 212°F (100°C).
    <1m
  2. Fill a pot with water.
    1m
WARNING

KEEP YOUR HANDS AND FACE AWAY FROM STEAM AND BOILING WATER BEFORE YOU TEST THE STEM.
Steam and boiling water can burn your skin in an instant.

  1. Heat the water to a full boil on the stove.
    7m
  2. Put the stem into the middle of the pot, to the depth you used for the ice slurry.
    • Do not let the stem touch the bottom or the sides of the pot.
    • Hold the thermometer with an oven mitt or a pot holder.
    <1m
  3. Wait until the reading becomes steady.
    1m
  4. Read the temperature while the stem stays in the pot.
    • A correct reading at sea level is 212°F (100°C).
    • Elevation lowers the boiling-point value by about 0.5°F (0.25°C) for every 500 feet (150 m).
    <1m
  5. If the reading needs a change, adjust it the same way as the ice-point test.
    1m
  6. Remove the thermometer from the pot with an oven mitt or a pot holder.
    <1m

After you finish

Estimated under a minute

NOTEA written record of your check helps you trust your next reading.
  1. Write down the final reading, the date, and any adjustment you made.
    <1m
  2. Stop and contact the manufacturer if the reading will not move to the ice point.
    <1m
  3. Repeat this check before an important use, or after a hard knock or a drop.
    <1m

Terminology

This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.

food thermometer
Also called: meat thermometer, probe thermometer, instant-read thermometer, cooking thermometer, kitchen thermometer
dial thermometer
Also called: bimetal thermometer, bi-metal thermometer, analog thermometer, stem thermometer, pocket thermometer
fridge or freezer thermometer
Also called: refrigerator thermometer, freezer thermometer, appliance thermometer, fridge thermometer
calibration nut
Also called: hex nut, adjustment nut, calibration screw, recalibration nut
ice point
Also called: freezing point of water, ice bath thermometer test, ice water thermometer test, 0 degrees C, 32 degrees F
calibrate a thermometer
Also called: calibrate a meat thermometer, adjust a dial thermometer, thermometer reading wrong, fridge thermometer accuracy, recalibrate a thermometer

When to use a professional

Stop if your thermometer reading will not move to 32°F (0°C) after you adjust it. Further adjustment can damage the mechanism. Contact the manufacturer or a calibration laboratory.

Stop if your thermometer has no calibration nut and no CAL function. Note the difference you found. Use it as a correction, or replace the thermometer.

Stop before you rely on this thermometer for food safety work if it fails this check. Undercooked meat, poultry, or egg dishes can carry harmful bacteria. Use a different thermometer that passes this check.

This page does not cover a certified calibration to a traceable standard. That work belongs to a calibration laboratory. Contact the manufacturer if you need a calibration certificate.

Common questions

How do I know if my meat thermometer is accurate?

Test it against a known temperature, called a fixed point. The easiest one to make at home is an ice-water slurry, which sits very close to 32°F (0°C). Put the stem in the slurry, wait for the reading to settle, and compare it with 32°F. If it reads within a few degrees, most cooks consider it close enough for kitchen use. If it is off by more, adjust it on a model with a calibration feature, or replace it.

What is the calibration nut on a dial thermometer, and does mine have one?

Many dial (bimetal) food thermometers have a small hex nut under the face of the dial. Turning it with a wrench or pliers moves the needle without opening the case. Not every dial thermometer has one, and not every one that has one can be turned easily by hand. CDN, a thermometer manufacturer, is explicit that this varies by model, so check your own thermometer's instructions rather than assume.

Can I calibrate a digital instant-read thermometer myself?

Some can, most cannot. A small number of digital models have a CAL button that resets the reading at the ice point, and CDN documents this feature on several of its own named models. Most inexpensive digital thermometers give a reader no way to adjust them at all. If yours has no CAL button or reset function in its own instructions, note the offset you found and use it as a mental correction, or contact the manufacturer.

Why does my ice-water test not read exactly 32 degrees?

A homemade ice-water slurry is close to the ice point but rarely exact. CDN's own instructions note that a slurry is more likely to read near 34°F (1°C) than a laboratory-precise 32°F (0°C), because a home kitchen rarely has enough ice for a fully saturated slurry. This is a property of the ice bath, not necessarily a fault in the thermometer. Use a generous 3-to-1 ratio of ice to water and let it stand for several minutes before you read it.

How do I check my refrigerator or freezer thermometer the same way?

Fridge and freezer thermometers are usually dial or digital thermometers too, and the ice-point check applies to both the same way it does to a food thermometer. The boiling-point method does not apply, because most appliance thermometers have a scale that does not reach 212°F (100°C). The FDA recommends keeping an inexpensive freestanding appliance thermometer in both the fridge and the freezer and checking them often, since the appliance's own control rarely shows the true temperature. See this site's page on setting a refrigerator and freezer temperature for what to do with the reading once you trust it.

How often should I recalibrate a food thermometer?

There is no single interval that fits every thermometer or every use. CDN, a thermometer manufacturer, states that a dial thermometer can lose accuracy after years of use or after a particularly hard jolt, without giving a fixed schedule. A reasonable habit is to check before an important use, such as a holiday roast, and always after a drop. If your thermometer fails the check and will not adjust back to the ice point, contact the manufacturer rather than keep using it for food safety work.

Sources

Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.

  1. Tier 1SI Units – TemperatureNational Institute of Standards and Technology (NIST) · accessed 2026-08-04 · re-verification due 2027-01-31
  2. Tier 1How to Recalibrate Your ThermometerCDN Measurement Tools (Component Design Northwest — thermometer, timer and scale manufacturer, founded 1984) · accessed 2026-08-04 · re-verification due 2027-01-31
  3. Tier 1FAQ — CDN Measurement ToolsCDN Measurement Tools (Component Design Northwest — thermometer, timer and scale manufacturer) · accessed 2026-08-04 · re-verification due 2027-01-31
  4. Tier 1Refrigerator Thermometers - Cold Facts about Food SafetyU.S. Food and Drug Administration · accessed 2026-07-29 · re-verification due 2027-01-25

Revision history

Current version 1 · updated 2026-08-04 · next review due 2027-08-04

  1. v1 · 2026-08-04First draft. Sourced to NIST's SI Units – Temperature page (the ordinary ice point, 0°C/32°F, distinguished explicitly from the triple point of water at 0.01°C, which the same page also states), two CDN Measurement Tools support pages (a real thermometer manufacturer, family-owned since 1984), and the existing FDA refrigerator-thermometers source for fridge/freezer applicability. The ice-point and boiling-point target temperatures and the elevation adjustment are published as verified, tier-1-sourced values. Whether a given thermometer has a calibration nut or a CAL function, and how far it can be adjusted, are published as consult-the-manufacturer instructions with no digit, because CDN's own documentation states this varies by model and most digital thermometers cannot be user-adjusted at all — matching the backlog note that this is per-model and not a fact this page can safely generalise. No competitor page was read or drafted from at any point (topic recorded from the backlog only). Scope is contact (dial and digital) food and fridge/freezer thermometers; infrared thermometers remain owned by check-an-infrared-thermometer per the existing rule-7 boundary note.

Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.

Comments and corrections

Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.

Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.

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