Types of Thermometers: Characteristics, Functions and Uses

A medical thermometer at home is a reliable way of measuring temperature when someone gets sick. You can accurately measure their temperature and figure out the steps ahead for their care.

However, with multiple types of thermometers out there, it is hard choosing the right one. And guesswork is the last thing you would want to do for safety.

So, what are the different types of thermometers, and which one should you get? Here is everything you need to know about the common thermometer types with their characteristics, functions, and uses!

1. Digital Thermometers


A digital thermometer works by using heat sensors to determine body temperature. They can take oral, rectal, and armpit readings. When using a digital one, do not forget that the armpit temperature runs about 0.5 to 1 to 1°F (0.6°C) cooler than oral readings, whereas rectal ones give a 0.5 to 1°F (0.6°C) warmer reading than oral ones. The tip of the device must be under the tongue with the mouth closed for accuracy.

A digital thermometer comes in handy to measure fever temperature. If you are a parent, we highly recommend having one that fits you the best.


  • They give you accurate readings in 1 minute or less.


  • Oral readings of it will not be accurate if taken too close to eating or drinking. The temperature can get skewed by food temperature. So, wait at least 15 minutes.
  • Rectal readings can be uncomfortable.
  • It can be expensive and requires battery replacement periodically. 

2. Tympanic thermometers


Tympanic thermometers employ infrared ray technology to measure the temperature inside the ear canal.

Tympanic temperature varies from 0.5°F (0.3°C) to 1°F (0.6°C) higher than oral temperatures. However, make sure that you have multiple of these as you cannot use one thermometer for all for hygienic reasons. Position it well for accurate measurements.


Tympanic thermometers provide fast and accurate readings. They are preferable to oral or rectal thermometers in children. However, we do not recommend them for infants under six months old. It is because their ear canals are too small to accommodate these tools without pain or discomfort.


  • Obstructions like earwax may skew results.
  • They may cause discomfort by not fitting well in small or curved ear canals.
  • They may worsen ear infections.

3. Forehead (Temporal) Thermometer


Forehead thermometers have infrared sensors to monitor the temperature of your superficial temporal artery. It is a branch of the carotid artery, a blood vessel. These are non-contact thermometers; they do not require physical contact and have gained popularity for use in places like airports, stores, and stadiums. Especially after the onset of the pandemic, all use it to identify potential Covid-19 patients with symptoms like fever.

The temperature in your forehead is about 1°F (0.6°C) lower than the temperature in your mouth.


  • Temporal thermometers provide accurate readings in a matter of seconds.
  • They are simple to use, and all infants, children, and adults can use them.
  • They allow you to accommodate multiple people with a single unit. As a result, you no longer need to empty your wallet on thermometers.


  • You have to position them correctly as per the manufacturer. Otherwise, they will not provide accurate readings.
  • External factors such as droughts, wind, indoor heating, and direct sunlight can all impact readings.
  • Wearing certain items such as hats or heavy coats can cause the results to be inaccurate.

4. Mercury (liquid in glass) Thermometer


Mercury thermometers were once the only way to take a temperature.

They are no longer widely accessible due to safety concerns. Some countries have even banned them and made them illegal to use.

This one bases itself on the principle of dilution of fluids. At high temperatures, liquids expand. These glass thermometers enclose liquid mercury. They have a calibration as per the melting and freezing points of water under atmospheric pressure. They show temperature ranges up to 110C mostly. Many people use them orally, under armpits, and rectally for measuring body temperature. People also use them in labs.


  • In atmospheric pressure, mercury thermometers provide accurate temperature readings.
  • You do not require batteries.


  • Mercury thermometers may break easily due to their glass construction, allowing toxic mercury to escape. They can also cause cuts.
  • You cannot throw mercury thermometers away because they contain a hazardous substance.
  • They can be hard to read.
  • The mercury should hold in place for 3 minutes for accuracy.

5. Alcohol (liquid in glass) Thermometer


An alcohol thermometer consists of a small sealed tube made of glass. A hollow bulb and a capillary opening are running through the length of its center. 

The bulb and connected capillary chamber have ethanol with nitrogen and ethanol vapors.

Along the length of the column, several marks show the temperature of the liquid at different volumes. Because ethanol is sensitive to temperature changes with a thin capillary to detect subtle shifts, there is a noticeable movement of alcohol. For ease of reading, the ethanol has a red dye.

It is for home use and is inexpensive.


  • It gives an easy reading.
  • You require no batteries.


  • The glass may break and hurt.
  • It is not very accurate.
  • It has a low range.

Non-Medical Thermometer Types 

There are other thermometers as well that exist for taking temperature measurements of other items. They work on two primary principles of contact and no contact. Often, they belong to the latter and use electrical quantities like resistance and infrared sensations through heat emission for results. Some names you might have heard may be:

  • Pyrometers, which are high-temperature thermometers that are useful in factories, baking ovens, etc. Have a look at our guide on 9 best ones for meat!
  • Bimetal foil thermometer: consisting of two metal foils with different coefficients of expansion.
  • Gas thermometers: they are very accurate thermometers that can be at pressure or constant volume.
  • Resistance thermometer: formed by a metal wire whose electrical resistance changes with temperature.
  • Thermocouple: used to measure temperatures based on the electromotive force generated by heating the two-metal weld.

What Thermometer Type is the Most Accurate?


The best thermometer is one that you can use correctly and comfortably. It is also a plus if your thermometer is by a reputable company.

Rectal thermometers are still widely regarded as the gold standard for babies and children by many medical professionals. Oral and forehead readings, on the other hand, are typically very reliable in these age groups.

For adults, we recommend infrared non-contact thermometers. Keep in mind that temperature readings vary depending on how you use the thermometer:

  • Rectal thermometer readings will be 0.5°F (0.3°C) to 1°F (0.6°C) higher than oral thermometer readings.
  • Oral temperature readings are typically 0.5°F (0.3°C) to 1°F (0.6°C) higher than tympanic thermometer readings.
  • Readings from axillary thermometers can be 0.5°F (0.3°C) to 1°F (0.6°C) lower than oral temperature readings (and maybe the least reliable).
  • Oral temperature readings are frequently 0.5°F (0.3°C) to 1°F (0.6°C) lower than temporal temperature readings.

The Bottomline

With our guide on the types of thermometers, you can now find the ones that fit you the best. If you want one for medical needs, do not go for non-medical ones. They not only give inaccurate results for fever but may also be harmful.

Stay tuned for our guides on how to choose the best baby, candy, and food thermometers.