How to calibrate a food thermometer: the ice-point check, when to do it and a log
Every temperature on your logs is only as good as the thermometer that took it. A probe that reads 4°F low turns a 44°F tray of chicken salad into a "pass". Nobody notices until an inspector's thermometer disagrees with yours.
Checking a probe takes two minutes and a cup of ice. This post gives you the rule, the steps, what to do when a probe is off, and a log to keep next to the thermometers.
General information, not food safety advice. Your thermometer's manual and your health department's rules come first.
What the Food Code asks
The FDA Food Code, the model code most state and local health departments adopt in some form, has four short rules on food thermometers:
- Have them. Food thermometers "shall be provided and readily accessible for use in ensuring attainment and maintenance of FOOD temperatures" (§4-302.12(A)). For thin foods, such as burgers and fish fillets, you need one "with a suitable small-diameter probe" (§4-302.12(B)).
- They have to be accurate. A thermometer scaled only in Fahrenheit "shall be accurate to ±2°F in the intended range of use" (§4-203.11(B)). One scaled in Celsius, or in both, has to be accurate to ±1°C (§4-203.11(A)).
- Calibrate them the maker's way. Food thermometers "shall be calibrated in accordance with manufacturer's specifications as necessary to ensure their accuracy" (§4-502.11(B)).
- Clean them. Equipment and utensils have to be cleaned "Before using or storing a FOOD TEMPERATURE MEASURING DEVICE" (§4-602.11(A)(4)).
So the Code doesn't set a method or a schedule. Your thermometer's manual does. Many thermometer manuals describe an ice-water check, because water with plenty of ice in it sits at the freezing point of water, 32°F (0°C).
The ice-point check, step by step
You need a tall cup or jar, ice (crushed or small cubes work best), cold drinking water, and the probe.
- Fill the cup to the top with ice, then add cold water until it just covers the ice. Packed ice matters: a few cubes floating in water aren't at 32°F.
- Stir and wait about a minute, so the water and ice settle at the same temperature.
- Put the probe in the middle of the cup, with the sensing area under the water. Keep it away from the sides and bottom. Most probes sense in the last inch or so of the stem; the manual says where.
- Stir gently and wait until the reading stops moving. A dial thermometer can take 30 seconds or more; a digital one a few seconds.
- Read it. You're looking for 32°F (0°C).
- Write the result on the log (below), even when it's right. A log of passes is what shows an inspector that you check.
Reading | What it means | What to do |
|---|---|---|
30°F to 34°F | Within ±2°F | In use. Log it. |
Below 30°F or above 34°F | Out of tolerance | Adjust it (below), or take it out of use |
No steady reading, or the display is dim | Battery or probe fault | Change the battery and check again; if still unsteady, replace it |
What about boiling water?
Some manuals also describe a boiling-water check. Water boils at 212°F at sea level, but at a lower temperature the higher you are, so the target depends on your altitude. Use it only if your manual gives you the number to expect. For a café that probes mostly cold food, the ice-point check is closest to the readings that matter, which are those near 41°F.
When a probe reads off
Follow the manual. In general:
- Dial (bimetal) thermometers usually have a calibration nut under the dial. Hold the nut with a small wrench or the tool in the sleeve, turn the dial until it reads 32°F in the ice water, and check again.
- Digital thermometers may have a calibration or reset function, or may not be adjustable at all. Some have to go back to the maker.
- Anything that can't be brought within ±2°F comes out of use. Label it Do not use and replace it. Keep a spare in the office so the kitchen is never without a working probe.
Then think about what it measured since its last good check. If a probe that read 5°F low was used for this week's cooling log, tell the manager. The logs may need a second look.
How often to check
The Food Code leaves the frequency to the manufacturer and to what's needed for accuracy. Many kitchens use a schedule like this:
When | Why |
|---|---|
When the thermometer is new | Find out before you trust it |
Once a week (or the frequency in the manual) | A routine catches slow drift |
After it's dropped, knocked or put through extreme heat or cold | A knock can move a dial; heat can damage a digital probe |
When a reading looks wrong | A cooler that "suddenly" reads 46°F may be fine; the probe may not |
Before a health inspection | So your readings agree with theirs |
Put the weekly check on the opening checklist for one day, Monday for example, so it has an owner.
The thermometer list
Number every food thermometer and keep a list. Unit thermometers (the ones mounted in coolers) aren't food thermometers, but check them against a calibrated probe as well, because the temperature log depends on them.
No. | Type | Where it lives | Scale | Adjustable? | Battery changed |
|---|---|---|---|---|---|
1 | Digital probe, thin tip | Line | °F | Reset button | |
2 | Dial probe | Prep | °F | Calibration nut | n/a |
3 | Digital probe (spare) | Office | °F / °C | No | |
4 | Walk-in unit thermometer | Walk-in, by the door | °F | No | n/a |
The calibration log
Date | Thermometer no. | Method | Reading | In range (30–34°F)? | Adjusted? | Reading after | Initials |
|---|---|---|---|---|---|---|---|
1 | Ice point | Yes / No | Yes / No | ||||
2 | Ice point | Yes / No | Yes / No | ||||
3 | Ice point | Yes / No | Yes / No | ||||
4 | Compared with probe 1 | Yes / No | n/a |
Keep the log with your other food safety records. When an inspector probes something, they may compare readings, and a log that shows weekly checks answers the question before it's asked. Our health inspection walkthrough covers the rest of the visit.
Habits that keep probes honest
- Clean and sanitize the probe before each use and before you put it away, and between raw and ready-to-eat food.
- Probe the thickest part of the food, away from bone and the pan.
- Give it time. Read once the number stops moving, not when it first looks good.
- Store it in its sleeve, away from the grill and the dish machine.
- Spare batteries in the office drawer. A dim display is the first sign of a wrong reading.
- Train it once: show each new hire the ice-point check during their first week, as part of station training.
Where Mays fits
- The check as a weekly task. In a checklist template, set Frequency to Weekly and tick the day, or Monthly with the dates. Add the check as a task. See Scheduling and assigning checklists.
- The log as a form with a pass range. An admin builds a Thermometer check form under Tasks → Types, with a Temperature field per thermometer and a pass range of 30 to 34°F. Each reading shows In range or Out of range in the app as it's entered. Add a Yes / No field for Adjusted?. Use Custom form as the task's answer type. See Building custom forms.
- The record. Every submitted form lands in Tasks → Data, one row per check, with Export CSV for the inspector. See Exporting task data.
What Mays doesn't do: there's no list of thermometers with their own history, so number them on the form's field labels and keep the list above on paper or in the knowledge base.
Two minutes, once a week
A cup of ice, a steady reading and a line on the log. Do it weekly and after every drop, take anything outside ±2°F out of use, and every other temperature you write down means what it says.
Start your free trial: 30 days, every module, no card needed. Or book a walkthrough and we'll build your thermometer check with you.