Learn More About Thermometers


A thermometer is one of those things you don’t always think about, but you’re happy to have one on hand when it’s needed. It’s great for cooking, keeping your house at the right temperature, and of course, checking to make sure you don’t have a high fever.

So the real question is… are you using your thermometer correctly? It’s time for a deep dive into thermometers. No medical degree required!

What is a Thermometer Used For?

You use a thermometer to measure temperature. Some countries, like the United States and the Bahamas, measure in degrees Fahrenheit. Everyone else measures in degrees Celsius. This is based on boiling and freezing points.

A thermometer’s job is to show you how close the temperature is to either boiling or freezing point. It can be used to check the temperature of all of the following:

  • People
  • Food
  • Buildings
  • Appliances
  • Water
  • Animals
  • Cars
  • Electronics


Are you feeling under the weather? A thermometer can be used to make sure you don’t have a fever, which according to the Centers for Disease Control and Prevention (CDC), is considered 100.4°F or higher.


The best chefs know you should check the temperature of chicken, pot roasts, pork chops, and other meat using a food-safe thermometer. Undercooked food may contain harmful bacteria like E. coli and salmonella.


Your house or apartment likely has a thermostat, which is basically a digital thermometer that reads the temperature of the room. It’s a handy device since you can adjust it to make the space colder or warmer.


Your refrigerator and freezer will be equipped with a thermometer. This helps you keep lunch meat, milk, and frozen pizzas from going bad. According to the U.S. Food and Drug Administration (FDA), you should keep your fridge at 40°F and your freezer at 0°F.


Jacuzzis, pools, and even some showers are equipped with a waterproof thermometer. This tells you the temperature of the water, so be sure to check how cold it is before you do a cannonball at the next pool party!


Your pets are staying safe thanks to the thermometer that’s fitted to most cages and aquariums. Reptiles need to be kept at 70°F to 85°F, while fish should swim in waters that are 76°F to 80°F.


Just like buildings, your car is fitted with a thermostat that reads the temperature. It tells you how hot your engine is running, which is important in keeping your vehicle safe while it’s on the road.


Almost every electronic device has a CPU (central processing unit) thermometer that shows how hot it’s running. If you have a bunch of programs open at once, your computer can completely fry if you don’t pay mind to your CPU thermometer!*

*DISCLAIMER: This isn’t an official diagnosis of why your computer might crash. Speak directly to an expert if you have any additional questions.

During the coronavirus (COVID-19) pandemic, thermometers were hard to come by. Some thermometers were even selling at over $100 on sites like Amazon and at drugstores like CVS.

How Does a Glass Thermometer Work?

A glass thermometer works due to the mercury or alcohol that’s filled inside. When the temperature gets warmer, the bulb underneath the mercury or alcohol expands and pushes the liquid up. As the temperature cools down, the bulb contracts which causes the liquid to naturally fall.

This infographic gives you an idea of how a glass thermometer works!

You’ve probably heard before that mercury is toxic, which is why it can be dangerous if your thermometer breaks. Mercury has been used for so long because its volume naturally changes with temperature in a noticeable way. Alcohol is considered a safer substitute and is much more commonly used in thermometers today.

Thermometers that have a red line are filled with alcohol, while ones with a silver line are filled with mercury.

How Do You Read a Glass Thermometer?

A glass thermometer can be a little tricky to read since it’s measured with lines. Hold the thermometer up to eye level, and see where the line ends. That will be your temperature.

You should read a glass thermometer at the closest line to get an idea of your temperature. The long lines indicate 1 degree, while the short lines indicate 0.2 degree.

Is a Digital or Mercury Thermometer More Accurate?

Digital thermometers are safer than mercury and are just as accurate. They work when an electromotive force (voltage) passes across a metal probe. The probe then measures how much current flows through it, and voila – you get a digital reading of your temperature on the screen!

Mercury thermometers can be used by adults since they’re made from glass and may contain a toxic substance. Digital thermometers, on the other hand, are much safer for kids.

How Do I Check My Temperature?

Doctors that work with patients may have a strategy for taking temperatures, but what about when you try it at home? It’s time for a quick lesson in how to use a thermometer!

You can check your temperature by putting the thermometer:

  1. Under your arm (axillary)
  2. Under your tongue (oral)
  3. In your ear (tympanic)
  4. In your rectum (rectal)
  5. Across your forehead (temporal artery)

How Much Time Should a Thermometer Be Kept Under Your Arm?

One of the easiest ways to take temperature is by sticking the thermometer under your arm in your armpit. You should hold your arm down for 7 to 10 minutes to get an accurate reading of your temperature, but it may vary depending on the manufacturer.

This is how to take your temperature under your arm:

  • #1: Grab a mercury thermometer and shake it until it falls below the 95°F mark. You can also use a digital thermometer if that works better for you.
  • #2: Tuck the bulb of the thermometer into the armpit and lower the arm over it. Note: This will be more accurate if you’re doing it with a bare torso.
  • #3: Hold the arm down for at least 7 minutes, or according to the instructions included with the thermometer.
  • #4: Look at the temperature and keep in mind it will be roughly 1°F lower than your actual temperature.

An axillary (underarm) temperature is a particularly great option for your child since it’s more comfortable than other methods. Make sure they’re holding still while the temperature is being read.

How Much Time Should a Thermometer Be Kept Under Your Tongue?

Most people prefer to take an oral temperature rather than using any other method. You should keep the thermometer under your tongue for 3 minutes if you’re using a glass thermometer and 30 seconds if you’re using a digital thermometer.

This is the proper way to take an oral temperature:

  • #1: Be sure that you haven’t eaten or drank anything in the last 20 minutes as this could affect the temperature reading.
  • #2: Place the tip of the thermometer in your mouth under your tongue. Keep your lips firmly closed while the thermometer is being read.
  • #3: For a digital thermometer, wait for 30 seconds until you hear the beep. For a glass thermometer, hold it still for 3 minutes.
  • #4: Read the thermometer for your temperature.

If you have the shivers, an oral temperature may not be as accurate as other methods. It’s also not a good idea to use this method if you’ve recently had dental work, or are having difficulty breathing.

How Do You Take an Ear Temperature?

You can use a tympanic thermometer to get your temperature. This is when you stick the digital thermometer in your ear rather than under your arm or tongue.

Here is how to take a temperature in your ear:

  • #1: Make sure you’ve been inside for the last 15 minutes before taking the temperature as being outside could affect an accurate reading.
  • #2: Slowly pull the top of the ear so you have access to the ear canal.
  • #3: Place the tip of the digital thermometer in your ear. The tip should be pointing to the space between the eye and the opposite ear.
  • #4: Wait for the beep and remove the thermometer to read the temperature.

Just like with an axillary thermometer, you may have a 1°F difference when you use a tympanic thermometer. Make sure you’re sitting still and patiently waiting for the beep.

How Do You Use a Temporal Artery Thermometer?

A temporal artery thermometer digitally reads your temperature from your forehead. These thermometers are sold at most retail stores.

Follow these steps when using a temporal artery thermometer:

  • #1: Place the probe on the center of the forehead.
  • #2: Press the button down and slide the probe in a straight line across your forehead to the hairline. Continue to hold the button down until the temperature is complete.
  • #3: Some thermometers may require you to also touch the soft spot behind your ear. Check the instructions.
  • #4: Remove the thermometer from your head and take note of your temperature.

Take a look at the package when you buy your temporal artery thermometer. There will likely be instructions for use printed on the box, or on a separate paper insert in the package. Don’t throw this away!

*DISCLAIMER: Quality Logo Products® is not a team of medical professionals. If you’re at all unsure on how to take temperature and if you have a fever, consult your doctor or a trusted physician directly for more information.

What is a Normal Body Temperature?

According to Cleveland Clinic, a medical center in Ohio, a normal body temperature is 98.6°F. You should call your doctor if your temperature is anywhere higher than 103°F.

If you do have a fever, medical experts at Healthline, Mayo Clinic, and Harvard Health recommend you do the following:

  • Call in sick.
  • Get some rest.
  • Drink plenty of water.
  • Eat light foods.
  • Keep things cool.
  • Take a lukewarm bath.
  • Contact your doctor.

Call in Sick

Nobody likes to take a sick day, but now’s not the time to be a hero. You need to focus on feeling better before you go back to the office or school. After all, you don’t want to pass on anything if you’re contagious.

Get Some Rest

Curl up in your bed and relax with a good book or a movie. You shouldn’t be exerting too much energy while you have a fever, so fluff up those pillows and take a chill pill!

Drink Plenty of Liquids

Water or orange juice should be your new best friends. Fill up a bottle or a glass and keep it on your nightstand. You can also suck on ice cubes if it’s too difficult to keep down liquids.

Eat Light Foods

You need your energy, so make sure you’re still eating throughout the day. Stick with foods that are easy to digest like yogurt, rice, toast, eggs, and oatmeal.

Keep Things Cool

Even if you have the chills, you should still try to cool down the room as much as possible. This includes putting on a fan, removing extra layers of clothing and blankets, and applying a cold compress to your forehead.

Take a Lukewarm Bath

Get the rubber duckies ready and soak in a bathtub filled with lukewarm water. Get out before the water gets frigid and dry off immediately.

Contact Your Doctor

Most medical experts recommend that you call the doctor if your fever is over 103°F. Reach out to a trusted physician for a proper diagnosis.

How Accurate Are Thermometers?

Thermometers aren’t foolproof. In fact, there may be a difference of up to 1°F, depending on which type of thermometer you’re using. This reading could also be affected if you’re not properly taking your temperature, if you’ve eaten recently, or if you have been outside all day.

Remember, you don’t have to rely on the thermometer alone. Your doctor is always available to help, so if you’re at all unsure, make an appointment as soon as possible.

The Bottom Line

A thermometer is a genius invention that not only keeps our refrigerators and pools nice and chilly, but can also help us figure out whether or not we have a fever. Be mindful that you’re always reading it accurately and that you’re making your health #1 priority!


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About the author

Alyssa Mertes

Alyssa is a promo expert with over four years of experience in the industry. She is the Lead Copywriter at Quality Logo Products and has had work published for the Promotional Products Association International and the Advertising Specialty Institute.