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How to Take a Temperature

How Do I Take a Temperature?

The best way to take a temperature is to use a digital thermometer. They are quick and easy to use. Do not use a glass mercury-containing thermometer. Mercury thermometers can be toxic if broken.

What is a fever? A fever is an increase in body temperature. A normal body temperature is around 98.6°F (37°C). In general, a fever is a temperature above 100.4°F (38°C).

What is a fever? A fever is an increase in body temperature. A normal body temperature is around 98.6°F (37°C). In general, a fever is a temperature above 100.4°F (38°C).

Fever Guidelines in Children

How fever is defined can vary based on the method used to take a temperature. Check with your doctor for specific fever guidelines.

How fever is defined can vary based on the method used to take a temperature. Check with your doctor for specific fever guidelines.

For children over 3 months of age, fever can be defined as:

  • An oral (by mouth) temperature of 100.9°F (38.3°C) or higher

  • An oral temperature of 100.4°F (38.0°C) or higher that persists for one hour 

  • An under the arm (axillary) temperature of 99.9°F (37.7°C)

  • An under the arm temperature of 99.4°F (37.4°C) or higher that persists for one hour

In a child younger than 3 months, a fever is an under the arm temperature of 99.4°F (37.4°C) or higher.

What Is the Best Way to Take a Temperature?

An oral temperature is generally the most accurate way to check for fever. If a child is too young or has painful mouth sores, take the temperature under the arm.

Oral and underarm temperatures are the two methods recommended for most pediatric cancer patients. Talk to your doctor before using any other method, such as temporal artery (forehead) thermometer or tympanic (ear) thermometer, since they may be less accurate. Avoid pacifier thermometers and forehead strips. They do not give accurate readings.

IMPORTANT: Taking a temperature rectally (in the bottom) can be a risk for pediatric cancer patients. Cancer patients often have weakened immune systems. They may have rashes or sores around the anus and bottom. A rectal thermometer can damage the thin skin of the anal area and increase risk for infection. Rectal temperatures are not usually used to check for fever in children with cancer.

For infants and young children who do not have cancer and who are otherwise healthy, pediatricians may recommend a rectal temperature. Rectal thermometers often provide the most accurate reading of body temperature. Always follow your doctor’s instructions on how to measure fever. 

How Do I Clean a Digital Thermometer?

Most thermometers can be cleaned using soap and water. You can also use rubbing alcohol (70% isopropyl alcohol) to wipe off the surface (rinse off before oral use). Wipe dry with a clean cloth.

Do not boil or soak the thermometer in water. Do not clean in the dishwasher. Always follow the directions from the manufacturer.

Find More Information on Fever and Taking a Temperature


Reviewed: August 2021