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How to Calibrate a Thermometer, Step by Step
Jan 12,2022
Learn how to test and adjust your thermometer for absolute accuracy—and you'll instantly become a better cook.

Now more than ever it's important to learn how to calibrate a thermometer. It's the height of summer, after all, and you're going to need to check the temperature of all those steaks you're grilling. For that perfect medium rare, you're going to need a tool that perfectly measures the temperature of the steak. Since we're not all so lucky to own the world's best and most accurate thermometer—which, btw, you should think about treating yourself to one—you're going to have to learn how to test and adjust your thermometer so it's backyard barbecue ready. Here's how:

1. What is Calibrating Your Thermometer?
Just like watches can run slow or fast, food thermometers are subject to inaccuracies with age and use. Thermometer accuracy can be affected by extreme temperature changes, like going from extremely hot food to cold food, or by being dropped or roughly handled. And if you're using your thermometer frequently, you may want to check it monthly just to make sure it's performing at its best. Luckily, you can test the accuracy of your thermometer and, in most cases, calibrate it to read accurately again.

2. How Do You Calibrate the Thermometer?
Many thermometers have a nut under their temperature dial that allows them to be adjusted, while most digital models have a reset button. You’ll want to check the package instructions of your device for exact instructions for calibrating your thermometer.

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 insure that you're getting a proper temperature read on your food. In this case, you can note the degree of inaccuracy and adjust your cooking temperature accordingly. For example, if the thermometer reads 2° higher than it should, always cook your food 2° higher than the recommended temperature on a recipe. Or, in seeing that your thermometer is inaccurate, you could buy a new one.

There are two methods for testing the accuracy of your thermometer and calibrating accordingly: You can calibrate it in extremely high temperatures or using extremely cold temperatures.

3. The Ice-Water Method
Fill a large glass with ice and then fill it with cold tap water. Stir the ice water and let it sit for 3 minutes. Place your thermometer in the ice water, making sure to stick the probe at least 2 inches into the mixture, but not to touch the sides or the bottom of the glass. Stir the ice water with the probe to even out the temperature of the water and prevent the probe from resting against an ice cube. Wait at least 30 seconds for the thermometer to read the temperature. The temperature on your thermometer should read 32°F or 0°C. If it does not, adjust the nut on the thermometer, turning the head until the needle lands on 32°F (or use the reset button as instructed).

4. The Boiling-Water Method
Bring water to a rolling boil in a deep saucepan. Place the stem of the thermometer in the boiling water. Again, make sure that it’s submerged at least 2 inches and wait at least 30 seconds. Your thermometer should read 212°F or 100°C. If it doesn’t, keeping the thermometer in the water, turn the adjusting knob until the needle reaches the 212°F mark.

NOTE: Remember that water boils at lower temperatures in high-altitude areas. If you live in a high-altitude area, adjust your test accordingly. Use this boiling point calculator as a guide.

At the end of this process, you will have a tool for measuring temperature that you can absolutely trust. And this accuracy isn't just useful for backyard grilling or searing steaks on your cast-iron skillet. Since you know your thermometer will read accurately, why not learn how to temper chocolate and make fancy molded chocolate for everyone in your life? Or you could make fudge? With tools that work, you can go forth and be bold in the kitchen.