How to Calibrate a Digital Thermometer: A Step By Step Guide

Accurate readings from our digital thermometers are incredibly important. They let us know when our food is ready to eat, what the temperature is like outside, and even our own temperature when we are feeling under the weather.

Could you imagine the danger of not heading to the hospital for a severe fever because your thermometer was giving a low, inaccurate reading? How about biting into freshly cooked chicken only to find an uncooked pink center when your thermometer clearly said it was at the right temperature?

Unfortunately, these temperature reading devices are not made to function correctly for a lifetime. At one point or another, they require recalibration to perform at an optimal level.

If you’ve found that your own seems a little off these days or are just wondering if it needs to be reset, we have put together a few simple steps that will teach you how to calibrate a digital thermometer for accurate readings every time. 

Here's How to Calibrate a Digital Thermometer

Step #1  Identifying the Need for Calibration

You may not know that your thermometer needs to be adjusted unless it is clearly giving an inaccurate reading. However, there are several times when your digital thermometer needs to be calibrated.

First Time Testing

One of the most important times that many tend to overlook is when you first purchase the product. Relying on an out of the box thermometer to give accurate results can leave you with a device that does not function properly from the get go.

Always make sure to adjust the reading on any new thermometer you buy!

After a Fall

Did you know that the impact from a fall can affect any thermometer’s ability to give a proper reading? Even a simple drop to the bathroom floor can knock things out of whack, causing improper readings when you really need them.

Calibrate any time after your model has taken a nose dive for the ground, especially if it landed on a hard surface.

Extreme Heat and Cold

While most personal users do not fall into this category, some may require a thermometer to measure extreme temperatures in their line of work. If you happen to use one for this purpose, it will need to be recalibrated after nearly every use to continue functioning correctly.

Frequent Use

Using your thermometer frequently for preparing meals or in times of sickness can cause it to give an off reading after a while. Calibrate your thermometer weekly if you are using it often to keep things as accurate as possible.

Knowing when to adjust the calibration on your digital thermometer will help you to keep it in tip top shape. If any of the above scenarios apply to you, then the next step is to begin testing for accuracy in the readings.

Step #2  Test Your Thermometer with Two Methods

To get your digital thermometer back on the right track you can either use the Freezing Point Method or the Boiling Point Method. You will have to use both to calibrate it fully and can choose either one you prefer to get the process started.

The Freezing Method

What you will need:

  • A glass
  • Water
  • Ice

Start by taking your glass and filling it up with ice cubes from your freezer, then add enough water so that the glass is nice and full. Next, you will want to stir the contents around to help the water become icy cold.

Afterward, wait at least three minutes to give the water time to match the temperature of the ice. Insert the thermometer’s sensor into the glass and allow roughly thirty seconds before checking the reading.

If it reads 32 degrees Fahrenheit, then it is functioning precisely as it should. Any other reading will tell you exactly how far off the temperature is so you can adjust it correctly in the next step.

calibrate digital thermometer ice - How to Calibrate a Digital Thermometer: A Step By Step Guide

The Boiling Point Method

What you will need:

  • Your stovetop
  • A cooking pot
  • Water

In this method, start by placing six inches of tap water into a cooking pan and bring it to a boil. Once the water is ready, place your thermometer’s sensor into the center of the body of water.

Make sure that the sensor is as close to the middle as possible, as placing it near the sides or bottom of the pot will negatively affect the temperature reading. You will need to hold it there for a minimum of thirty seconds so the reading can be taken.

If your thermometer is functioning properly, it will read a temperature of 212 degrees Fahrenheit, or 100 degrees Celsius. Just like the previous method, any different readings will let you know how much adjustment needs to be made in the following step.

calibrate digital thermometer boiling - How to Calibrate a Digital Thermometer: A Step By Step Guide
calibrate digital thermometer boiling - How to Calibrate a Digital Thermometer: A Step By Step Guide

Boiling Points for Different Elevations

It is important to note that the boiling point of water changes by altitude. 212/100 degrees F/C is right for anyone living less than 1,000 feet above sea level, but those living at higher elevations should expect different results.

If your location happens to be above the 1,000-foot threshold, then use this handy chart to determine what the thermometer’s reading should be.

  • 1,000 to 2,000 feet – 210/98.9 degrees F/C
  • 2,000 to 3,000 feet – 208/97.7 degrees F/C
  • 3,000 to 5,000 feet – 206/96.6 degrees F/C
  • 5,000 to 8,000 feet – 197.5/91.9 degrees F/C

Step #3  Calibration Itself

Learning how to calibrate your digital thermometer is a lot easier than you might think. You either need to turn a nut or press a button, that’s it!

Models with Nuts

Start by adjusting the nut of the digital thermometer to correct the temperature as needed, based on your findings with either the Freezing or Boiling Point methods. Simply turn the adjuster until the accurate reading is reached while the sensor is still in the water.

Models with Reset Buttons

Other models do not require a nut to adjust the reading, instead featuring a reset button. This will either be an incredibly small button that you will have to press in with a paperclip once you have located it or a larger button that you will press and hold while the sensor is in the water.

Once you have adjusted the reading to the appropriate freezing or boiling point, half the work has been done!

Step #4  Do the Opposite Test

If you chose The Boiling Point Method to calibrate your digital thermometer back in step two, you now need to do The Freezing Point Method. If you had chosen Freezing, then you will now do the Boiling test.

Follow the steps for the opposite method and test your thermometer once again on the other side of the temperature spectrum. You should find that it reads accurately, but may need to make minor adjustments if it is still off by some degrees.

It is important to use both tests because some thermometers differ in sensitivity at different ranges. Making sure both ends of the temperature spectrum are yielding the correct readings will ensure the most accurate response.

Step #5  Re-Calibrate If Necessary

If you do find that your thermometer hasn’t read the temperature correctly on the second test, follow the same instructions in Step Three to calibrate it once more by either turning the nut or holding down the reset button.

You may need to do this a few times before acquiring a perfect reading, but it will have been worth it when you need to rely on the accuracy of your digital thermometer in the future.

Alternative Methods and Laser Light Readings

There are a few other ways to check the accuracy of your thermometer depending on how many you own and what kind you use.

Multiple Thermometers

If you happen to own multiple thermometers, you can always cross-check the reading with a device that you know is properly calibrated.

The easiest way to go about this is using the Freezing Point Method on both of them, then comparing the results on the one you know needs adjustment and calibrating accordingly.

This method only works if you are positive that the thermometer used for cross checking is entirely accurate, but will save you time by not having to utilize the Boiling Point Method as well.

Red Light Thermometers

Many restaurants use laser light thermometers to measure incredibly hot and cold surfaces quickly. If you are concerned that yours is becoming uncalibrated, you can use the same two methods to determine its accuracy.

Always make sure to change the batteries, as this can cause readings to be off by several degrees. If that doesn't solve the problem, contact the manufacturer for further assistance.

Accurate Readings Matter

Whether you use your digital thermometer for personal use or require one for your workplace, it is of the utmost importance that they display an accurate reading on the screen every time.

These thermometers aren’t made to give perfect readings for a lifetime, and there a lot of factors that can cause them to become inaccurate. Thankfully, calibrating your digital thermometer is an easy and straightforward process.

With just a few household items, you can use the Boiling and Freezing Point methods to determine if your thermometer is calibrated correctly in a snap. If you find that it isn’t, adjusting the reading is as simple as turning a bolt or pressing a button.

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