Types of thermometer for fever

You may need to check or measure body temperature if you think you, your child, or someone else has a fever. 

A fever is a body temperature above 38℃ — this can be a sign that the body is fighting an illness or infection.

Using a thermometer is the best way to check for a fever. There are different types of thermometers, and they may:

• have different features
• be used in different ways
• have different levels of accuracy 

Your body temperature can vary depending on:

• your age
• the time of day 
• how you measure it
• whether or not you are unwell 

It’s a good idea to take your temperature when you feel well to give you an idea of your normal temperature. This way, you will have something to compare to when you feel sick.

Remember, fever is just one sign of illness. If you feel unwell, see your doctor or speak with a healthcare professional.

Read more about:

• fever in children
• fever in babies
• febrile seizures

You can measure body temperature using a thermometer designed for use in the:

• armpit — this is known as an axillary thermometer 
• mouth — this is known as an oral thermometer
• ear — this is known as a tympanic thermometer
• back passage or bottom — this is known as a rectal thermometer

You can buy most types of thermometers at your local pharmacy or supermarket.
Some thermometers work better for different age groups. To learn how to use your thermometer to get the most accurate reading, you can ask your:

• maternal and child health nurse
• doctor 
• pharmacist

When comparing temperature readings, always use the same type of thermometer in the same location of the body.

Digital 'stick' thermometers

Digital thermometers are quick to use and reasonably accurate. The silver tip or the thin end of the thermometer is the part that measures body temperature. Make sure it is held in the right place to get an accurate temperature reading.

There are multiple types of digital thermometers.

Axillary (under the arm)

Axillary (under the arm) thermometers are the preferred method of measuring temperature for babies younger than 3 months of age.

1. Place the thermometer tip in the centre of the armpit, when the skin is dry.
2. Place the baby's arm securely against their body.
3. Turn thermometer on and leave it in place for the time stated in the instructions. This is usually 3 minutes. 

Axillary thermometers may give a temperature lower than the core body temperature.

Oral (under the tongue)

Oral thermometers are useful for adults or children who are old enough to understand how to keep the thermometer under their tongue.

It’s important not to bite the thermometer, and to keep it in place for the time listed in the instructions. Do not use oral thermometers if your child is shivering.

1. Check the person hasn't had anything hot or cold to eat or drink for 20 minutes before you take an oral temperature.
2. Place the tip of the thermometer under the tongue and close the mouth and lips to keep the thermometer in place.
3. Turn thermometer on and wait until it beeps. 

Rectal (in the back passage)

Rectal thermometers provide the most accurate measurement of core body temperature. Using a rectal thermometer can be dangerous and distressing if the adult or child is moving around too much.

It’s important to disinfect your thermometer before and after use with warm, soapy water or an alcohol wipe.

1. Dab a small amount of lubricant on the end of the thermometer.
2. Carefully insert thermometer 2cm into the rectum (bottom).
3. Turn thermometer on. Wait for it to beep.  
4. Remove and clean the thermometer thoroughly. 

Tympanic (ear) thermometers

Tympanic thermometers take your temperature very quickly, so they are useful for adults or children who find it hard to sit still. They can be expensive, and the reading may not be accurate if the thermometer is not placed correctly in the ear. It’s important to follow the manufacturer's instructions carefully to get an accurate temperature reading.

1. Gently insert the probe into the ear canal with the tip facing the inside, towards the inner ear. Make sure the ear canal is totally sealed off.
2. Press the thermometer button and wait for the beep. You can then remove it and take the reading.

If the ears have been covered, such as with headphones, it’s important to remove these and wait until the ear canal is cool before measuring ear temperature.
If your baby's ear canals are too small to properly insert the probe, choose another type of thermometer.

Ear thermometers may give a temperature below the true core body temperature. 

Infrared thermometers

Infrared thermometers use an infrared scanner to measure body temperature without direct contact with the skin. You hold the scanner a few centimetres away from the body to take a temperature reading. They are also called digital temporal artery thermometers because they scan the arteries in your temple.

These are the easiest types of thermometers to use, but they can be inaccurate. 

Strip-type thermometers

Strip-type or plastic tape thermometers are placed on the forehead and change colour according to body temperature. They can be inaccurate.

Mercury thermometers

Do not use mercury thermometers. Mercury thermometers haven't been used in hospitals for many years and are generally no longer available to buy. They can break, releasing small shards of glass and highly poisonous mercury.

Sydney Children’s Hospitals Network (Opens in new tab) explains the signs, symptoms and treatment of fever (Opens in new tab).

The National Health and Medical Research Council has a fever fact sheet (Opens in new tab). 

Languages other than English

The Royal Children’s Hospital Melbourne (Opens in new tab) has a fact sheet on fever in children (Opens in new tab), in multiple languages. 

The Health Translations (Opens in new tab) page has information on fever (Opens in new tab) in languages other than English.