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Temperature, How to Measure: Brief Version

Where should I put the thermometer?

There are several ways to measure body temperature. Taking the temperature in the rectum is the most accurate. Taking temperature by mouth or ear is accurate if done properly. Using the armpit is the least accurate. Which you use may depend on your child's age:

  • With a baby less than 3 months old, a temporal artery or armpit temperature are best because they are safe and easy to do.
  • With a child less than 4 or 5 years old, you can use a rectal, temporal artery or electronic pacifier thermometer. You can use an ear thermometer after your child is 6 months old. You can get an idea of how your child is doing with the armpit, if you have to.
  • For a child over 4 or 5 years old, take the temperature by mouth, or use a temporal artery or ear thermometer.

How do I take a rectal temperature?

  • Have your child lie stomach down on your lap.
  • Put some water-based lubricating jelly on the end of the thermometer and on the rectum (the opening of the anus.)
  • Put the thermometer gently into the rectum about 1 inch. (If the child is less than 6 months old, put it in only about 1/4 to 1/2 inch.)
  • Hold your child still. Take the thermometer out when you hear the signal (usually a series of beeps).

Your child has a fever if the rectal temperature is over 100.4°F (38°C).

How do I take an armpit temperature?

  • Put the tip of the thermometer in an armpit. Make sure the armpit is dry.
  • Close the armpit by holding the elbow against the chest. Take the thermometer out when you hear the signal (usually a series of beeps).

Your child has a fever if the armpit temperature is over 99.0°F (37.2°C). If you have any doubt, take your child's temperature by the rectum.

How do I take a temperature by mouth?

  • Be sure your child has not had a cold or hot drink in the last 30 minutes.
  • Put the tip of the thermometer under one side of the tongue and toward the back. It's important to put it in the right way.
  • Have your child hold the thermometer in place with his lips and fingers (not teeth). Take the thermometer out when you hear the signal (usually a series of beeps).

Your child has a fever if the temperature is over 99.5°F (37.5°C) when taken by mouth.

How do I take a temperature using a pacifier thermometer?

  • Have your child suck on the pacifier until the temperature stops changing and you hear a beep. This usually takes 3 to 4 minutes.

Your child has a fever if the pacifier temperature is over 100°F (37.8°C).

How do I take an ear temperature?

  • If your child has been outdoors on a cold day, he needs to be inside for 15 minutes before taking the temperature.
  • Pull the ear backward to straighten the ear canal. Place the end of the thermometer into your child's ear canal and press the button.
  • It only takes about 2 seconds to take the temperature.

Your child has a fever if the temperature is over 100.4°F (38°C).

Written by Barton D. Schmitt, MD, author of “My Child Is Sick,” American Academy of Pediatrics Books.
Pediatric Advisor 2014.1 published by RelayHealth.
Last modified: 2012-05-15
Last reviewed: 2013-06-03
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
Copyright ©2014 McKesson Corporation and/or one of its subsidiaries. All rights reserved.
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