Which is the Most Accurate Thermometer I Can Buy?

Which thermometer is the most accurate?

My plan is to test myself for possible COVID-19 infection using a pulse oximeter and a thermometer. I did my research, and this is what I found out.

A tympanic type, a digital type, and certain forehead scanner thermometers are all accurate. The differences among them are speed and comfort. They are all accurate to within 2/100ths of a degree.

This information applies when measuring:

  • outside a hospital or diagnostic setting
  • anyone age three or older

These choices are accurate to within 2/100ths of a degree:

  • a tympanic ear probe thermometer
  • a digital rectum probe thermometer
  • a digital mouth probe thermometer
  • an FDA-cleared forehead scanner thermometer

What are the Different Types of Thermometers and Their Uses?

There are several ways to measure body temperature at home. Some are more accurate and safer than others are.

The safe and accurate thermometers are:

  • an ear thermometer
  • a digital thermometer goes in the mouth, rectum, or armpit
  • an FDA-cleared infrared forehead scanner thermometer

The glass mercury thermometer is accurate but unsafe.

The Tympanic Ear Thermometer

The tympanic is the most accurate because it gets an accurate reading at the best location.

A tympanic (ear) thermometer uses a metal probe to measure temperature inside the ear. It is minimally invasive, fast, and accurate to within 2/100ths of a degree.

The body’s temperature-regulation system is near the ear. Temperature measured at this location is the best representation of the body’s internal temperature.

The Digital Thermometer in the Rectum or the Mouth

A digital thermometer uses a metal probe to measure the target area’s heat. The rectum location is representative of the body’s internal temperature, but it is not necessary the digital thermometer rectally to get an accurate measurement!

Use a digital thermometer in the mouth for results that are accurate to within 2/100ths of a degree.

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Once you choose a location, stick with it. Never mix the target area between the rectum and mouth! Because: E. coli!

You can use a digital thermometer in the armpit, but it is the least accurate of the rectum, mouth, or armpit locations.

FDA Cleared Forehead Scanner Thermometers

If a manufacturer tests and documents its forehead scanner thermometer, it can get FDA clearance for that device. The FDA certifies the thermometer’s accuracy to within very tight limits.

You can purchase either an FDA-cleared or a non-cleared forehead thermometer. The only one I would purchase is FDA cleared. The error range in uncertified infrared thermometers is about 30%

I found many uncertified infrared thermometers that did not meet users’ expectations. I researched forehead thermometers that had at least 25 reviews and high customer ratings. Many had 20% or so 1-star reviews.

I did find one FDA-cleared, clinically tested forehead thermometer that I do recommend for accuracy. You can view it on the Recommended Products page.

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What is a Tympanic Ear Thermometer?

A tympanic ear thermometer scans the ear canal for heat. The temperature in the ear is a good representation of the body’s internal temperature. The body’s temperature-regulation system is near this target. The temperature found at the ear canal is most representative of the body’s internal temperature.

How Do I Take My Temperature with a Tympanic Ear Thermometer?

Safely remove earwax, which can alter ear thermometer results. Some ear thermometers compensate for wax blockage, but to get the best result, the ear should be clean.

Place the probe in the lower portion of the ear opening, on the intertragal notch. Within one to 5 seconds, the thermometer reports the temperature on its digital LED display.

How is a Tympanic Thermometer Superior to Other Types?

Extra features common in many ear thermometers include:

  • color-coded display (green is healthy, orange is high, and red is fever) based on person’s age (0-3 months; 3-36 months; 3 years-adult)
  • temperature history
  • disposable tip covers which eliminate the need to wash the device
  • a 3 second speed
  • a fever alarm

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Are Tympanic Thermometers Safe?

Tympanic thermometers are safe. I searched the FDA Medical Product Safety Network database for problems with tympanic thermometers. There were four reports since 2002. All appeared to be manufacturing issues. Four reports in 18 years of use means that they are safe.

Tympanic thermometers do not contain mercury, which is unsafe.


What is a Digital Thermometer?

If you do not know about the types of “digital thermometers,” you might end up buying the wrong one. The following thermometer types all use digital technology. You will sometimes find the word “digital” in their names and descriptions.

Only one is a “digital thermometer.” The digital stick thermometer is a metal probe on an electronic stick that displays the temperature on an LED screen.

  • a digital thermometer is a metal probe on a “stick” with an electronic display
  • a forehead thermometer is a gun shape device with an electronic display that beams infrared light at the forehead
  • a tympanic ear thermometer is a metal probe on a gun shape device with an electronic display

Most digital thermometers have a single toggle on/off button. You place the probe on the target area, wait about five seconds, and the device displays the temperature on the screen.

How is a Digital Thermometer Superior to Other Types?

Extra features on many digital thermometers include:

  • an alarm that beeps either at 100 deg. F. or a value you set
  • auto shutoff to save the battery
  • waterproof (touted as a feature but really, if it’s not waterproof, do not buy it!)
  • last reading recall even after turning the device off
  • a very quick readout

How Do I Take My Temperature with a Digital Thermometer?

Choose one target, and stick with it forever. The target is the mouth, the rectum, or the armpit. The rectum is accurate but uncomfortable and potentially dirty. The mouth is accurate and clean enough. The armpit is slightly less accurate but easy to clean up.

Never switch off where you use the thermometer. Theoretically, you can wash a rectal thermometer and use it in your mouth. If you screw up, you can get E. coli poisoning. Pick a designated location and mark the thermometer for that location.

Digital thermometers need a contact point to detect the temperature. The metal probe on the end is the contact point.

It’s important not to artificially overheat or cool the area before taking a temperature. Avoid soup and ice before using the thermometer in the mouth.

Some people who bite thermometers do not realize they’re doing that. Be mindful not to bite the device, but do close your lips around the stick.

Follow the washing instructions, and clean the thermometer immediately after using it. Store it in a container to prevent getting germs on the device.

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Are Digital Thermometers Safe?

Digital thermometers are safe. I searched the Medical Product Safety Network database from 2002 to 2020. Two digital thermometers showed up. Base on 18 years of data, they are very safe.

Digital thermometers do not contain mercury, which is unsafe.

What is an Infrared, No Touch, Forehead Thermometer?

A forehead thermometer is a gun-shape device that scans the forehead for infrared radiation (heat). It displays its results on an LED screen.

Because you beam the light from a distance, the forehead thermometer reduces the chance of cross contamination. This design is better at preventing the spread of germs through contact with the thermometer.

No-touch thermometers use the same technology as household heat loss scanners. In other words, aim it at a drafty area and it will tell you where the cold air is coming in. I’m serious. You can actually use your medical thermometer as a heat loss or hot spot scanner.

Just be aware that manufacturers calibrate thermal scanners to the target. All objects have a normal amount of heat they emanate. Those heat values are different for different objects. Metal emanates less heat than a forehead. If you use a forehead thermometer on metal, you’ll get an inaccurate result. If you use a metal thermometer on a forehead, you’ll get an inaccurate result.

How is a No-Touch Forehead Thermometer Superior?

Other features found on many forehead thermometers include:

  • backlit display viewable in the dark
  • incredibly fast one second results
  • color coded results (green is normal, orange is high, red is fever)
  • temperature history
  • automatic off
  • an alarm that triggers on a temperature you set

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How Does an Infrared (Non-Contact) Thermometer Work?

Infrared thermometers measure the infrared amplitude emitting from the surface. It measures the strength of the energy waves.

The forehead puts off heat in the form of infrared radiation. Infrared means it is just out of the visible range. Radiation means heat.

The radiation’s amplitude is the strength of the waves emanating from the forehead. The stronger the amplitude, the higher the temperature.

The temperature calculation is the measure amplitude (stronger with a fever) compared to the amplitude expected from a healthy person (weaker when healthy).


Are Infrared, No-Touch Thermometers Accurate?

FDA-cleared infrared no touch thermometers are accurate to 2/100ths of a degree. I have not yet found an accurate infrared thermometer that’s no FDA cleared.

It’s important not to use a baby or toddler thermometer on an adult. They have different calibrations. Infants and toddlers have different temperature ranges than those ages three through adult.

How Accurate is a Forehead Thermometer?

Doctors measure organ temperature during surgery. It’s not something anyone would ever do at home! Clinical decisions require this accuracy level. Studies show that infrared scanning is inferior to measuring the temperature of an internal organ with a metal probe. For home use, the FDA cleared infrared forehead thermometers are accurate to within 2/100ths of a degree.

Among digital, infrared, and ear thermometers, the competition is a mix. Each is very close to accurate.


Are Forehead Thermometers Safe?

Forehead thermometers are safe. I searched the Medical Product Safety Network database from 2002 to 2020. One infrared thermometer overheated. I have to believe this event was unique to this model, as there was only one infrared thermometer safety report in 18 years of data.

Forehead thermometers do not contain mercury, which is unsafe.


Do Forehead Thermometers Use Mercury?

Forehead thermometers do not use mercury. They use an infrared scanner that measures the heat emanating off the forehead.

How Can I Check My Temperature with an Infrared Thermometer?

First, only use an FDA-cleared infrared forehead thermometer. Uncertified thermometers are likely to be inaccurate.

Each manufacturer includes specific instructions their thermometer. You need to know:

  • the required angle of the device compared to the forehead (usually it’s “perpendicular”)
  • the required distance of the device from the forehead (usually it’s a matter of inches)

Can I Take My Body Temperature with a Household Infrared Thermometer?

You can take a body temperature with a household infrared scanner, but it will not be accurate.

You expect accurate results if you take a body temperature with an FDA-cleared, clinically tested infrared thermometer.

Infrared thermometers measure the heat emanating off an object. The thermometer’s software has to make assumptions about the object. What color is it? What is the “normal” temperature for this object? Exactly what is the infrared aiming at?

Do not use untested infrared or household infrared thermometers to measure body temperature.

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Are Ear, Digital, or Forehead Thermometers Better?

Tympanic (ear), digital (mouth), and FDA-cleared infrared (forehead) thermometers are very accurate for home use. They’re only slightly less accurate than a thermometer a doctor would use to make clinical decisions.

Tympanic, digital, and FDA-cleared infrared thermometers are accurate to within 2/100ths of a degree.

The tympanic thermometer works best if the ear is free of wax.

The digital thermometer works best if the mouth has not recently received ice or heat.

The forehead thermometer works best if it is FDA-cleared.

What is the Most Comfortable Home Thermometer?

The FDA-cleared forehead infrared scanning thermometer is the most comfortable. As a no-touch device, there is nothing to make you uncomfortable.

I don’t think anyone should bother buying a forehead thermometer that’s no FDA cleared.

The tympanic ear probe thermometer is the most accurate and is comfortable.

The digital stick mouth thermometer is accurate and is comfortable enough. It’s personal, of course, I think digital stick mouth thermometers are every so mildly annoying.

The digital stick rectal thermometer is the least comfortable, but it’s accurate.

What is a Normal Temperature on the Forehead and Body?

A normal forehead temperature is between 97 and 100 degrees. The 98.6 degrees Fahrenheit standard is only accurate for some people. Studies show that “normal” is in a range of three degrees.

Because of these new findings, you will get better thermometer results if you know three things:

  • body temperature is higher in the afternoon and evening
  • food and drink trick oral thermometers into giving inaccurate results
  • take temperatures when people are healthy, so you know what “normal” is when that person is sick.

(source, source)

What is the Dangerous Temperature for Adults?

102 deg. F. is a dangerous temperature in adults. Doctors at the Cleveland Clinic advise to treat a fever this high with a fever reducer. If that fails, you should contact medical help.


What Temperature is a Fever?

An adult has a fever is the temperature is 100 deg. F. or greater. However, because “normal temperature” is 97 to 100 degrees, someone with a temperature of 100 deg. F. might not have a fever!

It’s important to know the person’s temperature when they are healthy. When you measure the temperature when they are sick, you will know if it is abnormally high.


People Also Ask

Can I check my body temperature with my phone? Yes, but not that accurately. A smartphone temperature app is about 85% according to one anecdotal study.


Are battery-operated thermometers better than old glass mercury thermometers? The digital, forehead, and ear thermometers are all superior to mercury glass thermometers. This is because the digital, forehead, and tympanic thermometer:

  • does not contain mercury, which is highly toxic
  • is not made of breakable glass
  • is made of a hard plastic that doesn’t break easily
  • is much faster at bringing you a result
  • is capable of storing a history of readings
  • is capable of sounding an alarm

Photo by Anna Shvets from Pexels

About Caroline Bogart

Hello. My name is Caroline Bogart. I am a programmer, writer, and web developer. I build free websites for animal rescues. I was once featured in the Boston Globe. I am obssessed ways to avoid falling, saying mobile, and aging in place.

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