How to measure the temperature

There are four common methods of taking temperature. You can choose each of them to measure your temperature. The rectum is considered as the most accurate and reliable fever measurement site in medical science.

Sublingual / oral measurement (in the mouth)


To ensure that the reading is as accurate as possible, place the thermometer tip under the tongue to the left or right of the root of the tongue.

  • Use your lips to hold the thermometer tightly in place.
  • The sensor must have constant contact with tissue during the reading. It must be placed under the tongue in one of the two heat pockets at the back.
  • Keep the mouth closed during the reading and breathe evenly through the nose.
  • When your thermometer gives an acoustic signal, you can remove it from your mouth. If your fever thermometer does not have a beeping function, leave the thermometer in place for 3 minutes.
  • Do not eat or drink anything before the measurement, as this might influence the measurement result.
  • As a general rule, the oral temperature is 0.3 °C to 0.8 °C lower than the rectal temperature


The mouth is more easily accessible than other parts of the body.


Not recommended for babies and small children, as active participation is required during the measurement.

  • Distortion of the measurement values possible after consuming very hot or cold food, chewing of gum, smoking or through increased mouth breathing in a cold environment right before measuring.
  • If the nose is blocked, it is also hard to breathe during the measurement.

The oral thermometry method is a widely used method for taking the temperature. Do you still need a good fever thermometer to measure temperature orally? Try our Thermoval® fever thermometers! Thermoval® rapid for instance is entirely waterproof and well suited for all measuring sites. It is also equipped with the fast measurement technology which will give you the result of your oral measurement in only 10 to 30 seconds.


Rectal measurement (in the rectum)

  • The easiest way to perform this measurement is when the patient lies on their stomach.
  • You can lubricate the thermometer tip with any skin cream, although we recommend the use of perfume-free products.
  • Insert the thermometer tip carefully into the rectum. Do not insert any deeper than 2 cm at most.
  • Wait until the device beeps. If your fever thermometer does not have an acoustic signal, leave the thermometer in place for 3 minutes.


  • Temperature is not affected by outside influences.
  • No active participation of the baby is required.


  • Not easily accessible.
  • Uncomfortable especially for adults and older children.
  • Risk of cross contamination is higher if only one device is used in different individuals.

Rectal measurement is by far the most accurate method from a medical point of view, because it comes closest to the core body temperature. It is commonly used for babies and toddlers who cannot actively obey the instructions for oral measurement. Hygiene plays an important role with this measurement method. Thermoval® rapid, Thermoval® kids and Thermoval® kids flex are entirely waterproof and can thus be easily disinfected by soaking them in a disinfectant solution. Additionally, our Thermoval® kids thermometers can help you make taking temperature less stressful and a lot more playful. In addition, Thermoval® kids flex’s flexible tip guarantees safe and gentle measuring with small children and babies.

Axillary measurement (in the armpit)

  • Place the thermometer in the centre of your armpit and keep the arm close to the side of your body.
  • Wait until the device beeps. If your fever thermometer does not have an acoustic signal, leave the thermometer in place for 3 minutes.
  • Placing the thermometer in the armpit provides a measurement of surface temperature that can fluctuate by around 0.5 °C to 1.5 °C from the rectal temperature readings in adults.
  • Note that an exact reading cannot be obtained if, for example, the armpits have been allowed to cool. If this is the case, we recommend extending the measurement time to 5 minutes in order to obtain the most precise reading possible.


  • Very simple.
  • No need to insert the device into any orifice of the body.


  • Significantly affected by peripheral cooling.
  • Often provides inaccurate readings.

The axillary thermometry method is a very old method and is still commonly used in the households. For accurate results with this measuring technology, it is essential to have a good fever thermometer. The Thermoval® family stands for reliability and accuracy. Thermoval® standard suits the simplicity of this measuring method. You want a quick result? Try Thermoval® rapid! If you are measuring in children, you might want to take a look at our children’s range, Thermoval® kids and Thermoval® kids flex which were especially designed to fit our smallest patients’ needs.

Tympanic membrane measurement (inside the ear)

  • The measurement can be carried out in the right-hand or left-hand ear.
  • The thermometer measures the infrared rays emitted by the eardrum and the ear canal. These rays are picked up by the sensor and converted into temperature values. The best values are obtained when the infrared rays are picked up from the middle ear (eardrum). Rays which are emitted from surrounding tissue produce lower measured values.
  • Stretch the ear canal by pulling the middle of the outer ear to the back and up at the same time. In case of children below the age of one year, pull the outer ear to the back only. Carefully insert the thermometer tip into the ear canal until you feel a slight resistance.
  • In a matter of seconds, the device beeps and the measurement is completed.
  • The temperature values may vary from ear to ear. For this reason, please always use the same ear.
  • The measurement must not be carried out in an ear which is suffering from inflammatory diseases as well as after ear injuries (such as eardrum injury) or during the healing phase after a surgical procedure. If medication has been applied to an ear, this ear must not be used for measurement either.


  • Gives results close to the actual core body temperature.
  • Very fast procedure and effective.
  • This method is good to use for babies and also for adults.
  • Mostly used in hospitals and clinics.


  • It is hard to determine if the temperature is from eardrum or some other areas of the ear canal.
  • If earwax accumulates on the measuring sensor, this may lead to inaccuracies of the temperature measurement or may even cause an infection between various users. For this reason, it is imperative that the measuring sensor is cleaned for every measurement.

The ear measurement is one of the fastest and most accurate methods to measure body temperature – and surely it is the most gentle way to take your little one’s temperature. This method is non-invasive, quick and painless. Once you have tried our Thermoval® duo scan ear measurement thermometer, you will never want to return to normal digital fever thermometers ever again. Our Thermoval® duo scan even combines the ear method with the forehead measuring method! Even if your child suffers from an ear infection, you can still monitor its temperature easily, without having to worry about causing damage or pain.

Temporal artery measurement (on the forehead)

  • The thermometer measures the infrared radiation emitted by the skin in the forehead and temple area and the surrounding tissue. The radiation is picked up by the sensor and converted into temperature values.
  • The most precise values are obtained when you scan the area over the eyebrows towards the temple.
  • Position the surface of the forehead adapter about 1 cm over the middle of the eyebrows.
  • Move the thermometer along the forehead towards the temple.
  • When the device beeps, the measurement is completed.
  • Remove hair, perspiration, cosmetics or dirt from the forehead to ensure optimum in measuring accuracy.


  • Easy to use and very fast.
  • No active participation needed.
  • It is possible to take temperature even when the baby is sleeping.
  • There is no need to insert the device into mouth, rectum or ear.


  • The temperature may be influenced by external environment.

This new measuring method allows you to monitor fever in your baby’s sleep! The movement of the infrared thermometer Thermoval® duo scan over your child’s skin is not more than a soft caress and will not disturb his or her slumber. Let your child rest while you watch over it with Thermoval® duo scan. Thermoval® duo scan combines the renowned ear measurement method with the modern forehead measurement and gives you maximal security with the measuring results.



Useful tips for taking temperature:
  • Do not leave your child alone when the thermometer is in place.
  • Mark fever thermometers for rectal, oral and armpit readings. Never use a thermometer used to take a rectal temperature for oral measurement.
  • Read the instruction manual before using a fever thermometer.
  • Choose thermometers that are easy for you to use.
  • Clean the thermometer after each use as advised by the manufacturer.
  • It is not recommended to take oral temperature when the patient’s nose is blocked. Choose the rectal or armpit method instead (also possible: Ear or forehead measurement).
  • Only take the temperature 10 minutes after the patient has last smoked a cigarette, eaten or drunk hot or cold beverages.
  • It is important to read decimal places correctly when you call the doctor.