Why do I need a thermometer?

You may need to measure body temperature if you think you, your child, or someone else has a fever. A fever is a body temperature above 38℃ and can be a sign that the body is fighting off illness or infection.

Use a thermometer to check for a fever. There are different types of thermometers, and they have different features.

Normal body temperature can vary depending on age, time of day and how you measure it. Take your temperature when you feel well to give you an idea of your normal temperature range. This way, you will have something to compare to when you feel sick.

Remember that fever is just one sign of illness, and your body temperature is not always the most important measure of how sick you are. Check all your symptoms and see your doctor if you feel unwell.

Read more about:

• fever in children
• fever in babies
• febrile seizures

How do I measure body temperature?

You can measure someone’s body temperature in different ways and the results can vary depending on the type of thermometer you use. Always follow the manufacturer's directions.

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

• armpit (axillary)
• mouth (oral)
• ear (tympanic)
• back passage or bottom (rectal)

Most types of thermometers are available for sale at your local pharmacy or supermarket.

Some thermometers and methods work better for different age groups. Ask your Maternal and Child Health Nurse, GP or pharmacist to show you how to use your thermometer to get the most accurate reading for your child.

When comparing measurements, always use the same type of thermometer in the same location on the body.

What are the different types of thermometers and why might I choose them?

Digital 'stick' thermometers

Digital thermometers are quick to use and reasonably accurate. You can used them under the arm (in the armpit) or under the tongue. 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.

Under the arm (axillary)

Under the arm (axillary) digital thermometer is the preferred method for babies younger than 3 months of age.

1. Place 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 the thermometer in place for the time stated in the manufacturer's instructions.

Under the tongue (oral)

Under the tongue (oral) digital thermometer is 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 amount of 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 under their tongue and ask them to close their mouth and lips to keep the thermometer in place.
3. Turn thermometer on and wait until it beeps.

In the back passage (rectal)

In the back passage (rectal) is the most accurate measurement of core body temperature. It can be dangerous and distressing if the adult or child is moving around too much.

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

Ear (tympanic) thermometers

Ear 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. Follow the manufacturer's instructions carefully to get an accurate temperature reading.

1. Gently insert the probe into 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.

If ears have been covered (for example, with headphones or a beanie), remove the items and wait until the ear canal is cool before measuring the ear temperature.

If your baby's ear canals are too small to properly insert the probe, choose another type of thermometer.

Infrared thermometers

These 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 read temperature. 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 are not generally very accurate.

Mercury thermometers

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

Resources and support

• For information on looking after a child with a fever, visit the Queensland Health Fever in Children factsheet.
• Sydney Children’s Hospitals Network explains fever signs and symptoms, as well as treatment.
• Call the healthdirect helpline on 1800 022 222 at any time to speak to a registered nurse (known as NURSE-ON-CALL in Victoria) for more information and advice.
• Call Pregnancy, Birth and Baby to speak to a maternal child health nurse on 1800 882 436 or video call. Available from 7 am to midnight (AET), 7 days a week (including public holidays).

Other languages

For more information in different community languages, the Royal Children’s Hospital has translated fact sheets on fever in children.