Last updated: August 11, 2021

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Clinical thermometers are very useful devices for checking body temperature. In case of illness, it is very advisable to check the temperature regularly - especially for children. If you don't have a clinical thermometer at home, you should buy one. But what are the different types and what criteria should you consider when buying one?

In our clinical thermometer test 2022, we present the best and most up-to-date clinical thermometers in the various categories. We also give you useful information and interesting facts about clinical thermometers. Whether you choose an extension thermometer, digital clinical thermometer or infrared clinical thermometer, you will find the best clinical thermometers on the market.


  • A clinical thermometer shows your maximum body temperature up to 42 degrees and thus gives you an indication of a possible fever.
  • You can choose between classic or digital thermometers, whereby the digital devices also include infrared thermometers.
  • Fever measuring devices can be used axillary, rectal, oral or even in the ear or on the forehead. The most accurate measurements are taken in the buttocks.

The Best Clinical Thermometer in the United Kingdom: Our Choices

Guide: Questions you should ask yourself before buying a clinical thermometer

What should a thermometer show and what types are there?

Your thermometer shows you whether you have a fever and if so, how high it is. There are classic glass thermometers and digital thermometers. The latter also includes infrared thermometers. A clinical thermometer measures your body temperature between 35 and 42 degrees and should always show your maximum temperature. Mercury thermometers, for example, fulfil this criterion.

However, since a thermometer filled with mercury easily becomes defective and is difficult to dispose of, these glass thermometers often contain galinstan as a liquid instead. But also digital thermometers with batteries are often used, because they show your value quickly and legibly on an LED display.

Don't forget the infrared thermometers, which measure the radiation by means of a sensor without contact or by touch.

Anzeige eines digitalen Thermometers

There are different types of thermometers that you can use to determine whether you have a fever and how high it is. Here you can see a digital thermometer, where the value is displayed directly and does not have to be read off a scale as is the case with analogue models. (Photo: Myriams photos /

Where on the body do fever thermometers measure, and how long and accurately are they measured at each location?

Fever thermometers can be used under the armpit, in the mouth, in the ear, on the forehead or rectally. The most accurate and shortest measurements are taken at the last three places mentioned. Basically, you can put the thermometer under your armpit.

This is a popular spot, but it also gives the least accurate maximum reading and takes the longest, about 8 minutes. However, the thermometer in the mouth, i.e. orally, is even less accurate and can take up to 5 minutes. The best and quickest method is therefore to use a clinical thermometer for the bottom.

Ear thermometers and non-contact forehead thermometers are also good thermometers for taking a quick temperature.

For babies and toddlers, it is best to use the rectal method, as this is the most reliable.

How much does a clinical thermometer cost on average?

In general, you can expect a price between 5 and 50 euros. However, the price of a thermometer does not depend on the accuracy of the measurement. Even inexpensive devices can take very precise measurements. The differences in cost are mainly related to the part of the body you want to use the device on, the extras, the age and where you buy it.

Thermometers for the buttocks and children are cheaper than infrared devices for the ear or forehead for adults. Furthermore, the devices are often cheaper on the internet than in an electrical shop.

Decision: What types of clinical thermometers are there and which is the right one for you?

Basically, you can distinguish between three types of thermometers:

  • Extension thermometer
  • Digital clinical thermometer
  • Infrared clinical thermometer

Due to the design and the type of built-in sensor, the respective functioning of these types of clinical thermometers is very different. Therefore, there are different advantages and disadvantages for each of these types of construction. Depending on your preference and intended use, a particular model is best suited for you.


Depending on your preference, either an extension thermometer, a digital clinical thermometer or an infrared clinical thermometer is suitable for you

The following section briefly explains the differences between the various types of thermometers so that you can decide for yourself which thermometer is right for you. In addition, the advantages and disadvantages of each type are clearly listed.

Special types of thermometers, such as the quick fever test or the dummy thermometer, are not mentioned further on this page. These are special forms of measuring the body's temperature that are not very accurate in their measurement and cannot be categorised into one of the three defined types.

How does an expansion thermometer work and what are its advantages and disadvantages?

An expansion thermometer is a contact thermometer that is equipped with a so-called thermometer liquid that is located in a capillary inside the measuring instrument. Due to the heat generated at the measuring tip, the liquid expands and shows the measured temperature on a display.

The measuring time is several minutes. Handling can be described as unwieldy, as the measuring pointer must be moved to the original position after each use by repeatedly tapping the outside of the glass of the clinical thermometer with the finger or shaking it. In the past, mercury was used as the thermometer fluid in these measuring instruments.

However, this has been banned for use in measuring instruments in the EU since April 2009, as mercury is classified as highly toxic. Therefore, galinstan is now the liquid used in many expansion thermometers.

  • Very cheap
  • Long shelf life
  • Can break
  • Unhandy to use
  • Long measuring time

How does a digital clinical thermometer work and what are its advantages and disadvantages?

A digital clinical thermometer is a contact thermometer that is operated without thermometer fluid. Instead, you need a small battery, usually a small button cell, to operate it. The sensor in these models is electric and measures the desired temperature orally, rectally and axillary at the touch of a button.

The operation is very simple and relatively fast, because the electronic display in the digital thermometer works independently and automatically, in contrast to the mechanical display in the extension thermometer. Also, the measuring time with this type of temperature measurement is by far not as long as with a mechanical device.

Normally, the measurement takes one minute.

  • Relatively inexpensive
  • Easy to use
  • Battery required
  • Relatively long measuring time

How does an infrared clinical thermometer work and what are its advantages and disadvantages?

The way an infrared clinical thermometer works is not dissimilar to that of a digital thermometer. However, unlike the other measuring devices, direct skin contact with a measuring tip is not necessary. The only exception is the infrared ear thermometer, whose measuring tip must be placed in front of the ear canal.

Infrared thermometers are very popular and frequently used, especially in the medical and clinical field, because the measurement results are very precise and the measurement time is very short. In the meantime, there are also infrared measuring devices for household use that can be purchased at lower prices.

  • Very precise measurement results
  • Short measurement duration
  • Relatively expensive

Here you can find an overview of all three types of clinical thermometers:

Clinical thermometer Description
Expansion thermometer Expansion thermometers are durable and cheap. However, they can break, are awkward to use and take a long time to measure.
Digital clinical thermometer Digital clinical thermometers are easy to use and cheap. However, they need batteries and a long time to take a reading.
Infrared clinical thermometer Infrared clinical thermometers measure very accurately in a short time. But they cost a lot.

Buying criteria: You can use these criteria to compare and evaluate fever thermometers

In the following, we would like to show you how to compare and evaluate different clinical thermometers. This will make it easier for you to choose the right additional product for you. In summary, the following criteria should be distinguished:

  • Type of clinical thermometer / place of measurement / age group
  • Weight / Measuring time / Memory / Battery operation
  • Signal tone / Fever warning / Water impermeability
  • Protective caps / Storage box

In addition, you must also pay attention to the individual special features of the thermometers, as well as their measuring accuracy, ease of cleaning and disposal. In the following paragraphs, you can read about the significance of these individual characteristics in order to be able to better compare the different devices with each other.

Type of thermometer / place of measurement / age group

The type of measurement means whether the thermometer is a glass thermometer, a classic digital thermometer or even a digital infrared thermometer.

While the infrared as well as glass thermometers are mainly used by adults, you can use the classic digital devices mainly for babies, toddlers and children to measure in the buttocks. In principle, however, many clinical thermometers can be used for any age group.

Weight / measuring time / memory / battery operation

These criteria are very important when buying a clinical thermometer. The device should be small and handy for you, guarantee a quick measurement, possibly also be able to save the values and be operated digitally for simplicity. You can expect digital devices with battery operation to be easy to use.

However, not all of these devices can store the measured values and thus make them comparable for you. For those that can, however, you have access to approximately the last 20 values.

Signal tone / fever warning / water impermeability

The thermometer will beep loudly to let you know when the measurement is finished. If there is also a fever warning as an additional function, there is nothing that stands in the way of your purchase.

A fever warning means that you can enter the limit value ahead of time and if this limit value is exceeded, the device will indicate your temperature by flashing or beeping. Sometimes the fever monitor is also waterproof.

Protective caps / storage box

If you don't want to spend too much on your thermometer, you should check beforehand whether protective caps or boxes are included free of shipping costs with the purchase of the device. Often, boxes for storage are automatically included with the purchase of a thermometer.

You can find out about their size and design from the manufacturer or the seller. Disposable protective caps are sometimes also included for ear thermometers, which makes the measurement more hygienic.


Most clinical thermometers, as shown here especially for the ear and head, come with a protective cap.

Special features of the thermometer

Special features of the thermometer, such as various additional functions, make its purchase particularly recommendable. Additional functions can be an automatic switch-off technique or a flexible tip of the thermometer. This also includes age-related temperature measurement, where the measured value can be determined for the set age.

Measurement accuracy / easy cleaning / disposal

Accurate measurement, easy and quick cleaning and an environmentally friendly throw-away policy or reuse of the thermometer or its parts are also important. If you want to be on the safe side when it comes to measuring accuracy, you should attach importance to pre-warmed measuring tips or the calibration of the thermometer.

Certification as a medically usable thermometer does the rest. Disposable protective caps for the tip of the thermometer are important for hygiene and disposal.

Facts worth knowing about clinical thermometers

What is the history of the clinical thermometer?

Daniel Gabriel Fahrenheit was the first inventor of the clinical thermometer in 1714, but because it was about 60 cm long at the time, it was unwieldy and the measurement was not accurate.

Did you know that the company Blue Spark Technologies developed the world's first "portable Bluetooth clinical thermometer"? This is a soft, comfortable, disposable patch that continuously takes temperature readings wirelessly. Additionally, when the patient reaches a temperature threshold previously set by the user, the body-worn patch can send alerts to mobile devices.

In 1867, a doctor from England named Thomas Clifford Allbutt took on this problem and invented the shorter and now-popular 15 cm clinical thermometer. A year later, the short thermometer was converted into a maximum thermometer, where the maximum value could be read long after the measurement had been taken.

In 1890, the modern clinical thermometer by Wilhelm Uebe came onto the market, which made the measurement more hygienic due to the tight closure.


The clinical thermometer as we know it today has not been around for very long. However, earlier precursors already existed in the 18th century.

How can you disinfect a clinical thermometer?

Especially when measuring in the buttocks or mouth, you must make sure that the thermometer is cleaned accurately. We can recommend the following:

  • Cleaning with cold soapy water
  • Cleaning with warm soapy water and rinsing necessary
  • Cleaning with cotton wool, cloth or tissue and alcohol

Sometimes you can buy clinical thermometers with hygienic sleeves. For infrared devices for the ear, there are special protective caps for one-time use.

Image source: / Parinya Binsuk