Calibrating a thermometer may be a simple, but necessary process. If you’re anything like me, you’ve probably got a couple of thermometers dancing around your drawer of miscellaneous kitchen tools. But are they accurate? How Do You Calibrate a Thermometer in general? Keep reading!

If you’re roasting a turkey, a degree or two of inaccuracy isn’t getting to make a dramatic difference. How do you calibrate a thermometer in general? Keeping read!

But, if you’re making caramel, tempering chocolate, cooking sous video, grilling a steak, or doing any number of other tasks that need a particular temperature, having a thermometer you’ll trust is clutch.

Calibrating your thermometer is quick and easy. Many analog and digital thermometers allow you to offset the temperature to regulate for the calibrated value. However, if your thermometer doesn’t offer an offset function, a bit of blue tape with the delta will work just fine.

METHOD 1: ICE WATER

1. Fill a glass with ice cubes, and then top off with cold water.

2. Stir the water and let sit for 3 minutes.

3. Stir again, and then insert your thermometer into the glass, making sure not to touch the sides.

4. The temperature should read 32°F (0°C). Record the difference and offset your thermometer as appropriate.

METHOD 2: BOILING WATER

1. Boil a pot of distilled water.

2. Once the water has reached a rolling boil, insert your thermometer, making sure not to touch the sides or bottom of the pot.

3. The temperature should read 212°F (100°C). Record the difference and offset your thermometer as appropriate.

Why It’s Important to Calibrate Your Thermometer

Calibration gives you the peace of mind of knowing the temperature you’re reading is that the correct temperature of the media you’re measuring. That can be extremely important for procedures that require precise temperature control, including industrial chemical processes and food preparation.

Many cities and state health departments have food storage guidelines with strict temperature ranges which edibles can’t deviate from. Beyond the regulations, you don’t want anyone to urge sick because your thermometer said your pork ribs were 145° F once they were only 110° F.

Obviously, that is extreme example. A thermometer that far off of register would likely need to replace.

A thermometer should register within 2° F of actual temperature to be considered accurate. That 1.1° C.

Testing should be done regularly, counting on the frequency of use and therefore the thermometer’s purpose. Thermometers used for processes that require precise measurements should be tested daily or weekly. If a thermometer goes out of calibration often. The replacement may be necessary.

How do You Calibrate a Thermometer

There are a couple of alternative ways to calibrate digital and bi-metal thermometers.

The most common are comparison boiling and freezing. There also are thermometer calibration services that will do that for a price.

Liquid in glass thermometers should sold by direct material. Feature an adjustment screw on the rear of the dial.

Note that, if your thermometer doesn’t have an adjusting nut (or calibration screw, etc., usually found on the rear of the thermometer, you’ll need to send it to one of these services for re calibration.

Although you can mark specific temperatures (Boiling and freezing point can be marked on thermometer casing with tape) with the following methods, a full range of temperatures may not be achieved.

The duration choice bi-metal thermometers we sell have an optional calibration dial located on the rear of the dial case.

The first and simplest method is by using comparison. That is, compare the thermometer you think might need re-calibration to a thermometer which has already been calibrated or that has been a national institute of standards and technology (NIST) certified.

Which is Why an NIST-Certified Thermometer

This method is often effective, goodbye as you’re confident that the comparison thermometer is reading correctly. Which is why a NIST-certified thermometer, tested annually, is preferable?

Just compare the 2 and adjust the thermometer you’re calibrating to match the “correct” thermometer’s temperature.

This should do with distilled water, as tap water has compounds in it which could affect the freezing or melting points of water and skew the process.

Calibration ice water or “Freezing” the thermometer is best for thermometers used to measure low temperatures. Add crushed ice to a bowl or cup of water to make a slushy mix a minimum of 2” deep. Insert the thermometer stem into the slushy mix, for at least one minute.

Make sure the stem does not come into contact with the sides or bottom of the container. The thermometer should read believe 30 and 34° F. if it doesn’t adjust the dial 32° F.

To calibrate a thermometer won’t measure higher temperatures. You might prefer the boiling method. Again, use distilled water and bring it to a rolling boil in a pot or breaker if you have one handy.

Insert the thermometer’s stem a minimum of 2” into the water for a few minutes, taking care to not burn you while doing this. Do not let the stem touch the edges or bottom of the container. The thermometer should read between 210 and 214. If it does not, adjust the dial to 212F.

That boiling point is at sea level. But since the boiling point changes at different altitudes, you will need to consult a chart like this one to determine the correct boiling point for your elevation. You can find your elevation here.

Final Thoughts

When a change of this type does take place, the indication of the thermometer will also change. Re-calibration of the certified thermometer updates the indications and thus allows the user to maintain accurate, reliable, and consistent results when making temperature measurements.

In rare cases, thermometers can’t be calibrated. Even if your thermometer can’t be calibrated, you can – and should – use these methods to check its accuracy and ensure that you’re getting a proper temperature read on your food.

Thermometers used frequently must be calibrated frequently (weekly or monthly). Follow the manufacturer’s instructions for taking temperatures.

Always calibrate a new thermometer, one that has been dropped on a hard surface, or one with a temperature reading that is off by more than +/- 2°F (+/-0.5°C).