How to Measure a Temperature

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, use the armpit. It's easier and safer.
• With a child less than 4 or 5 years old, using the rectum is the best. 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.

How do I take a rectal temperature?

• Have your child lie stomach down on your lap.
• Put some petroleum 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. If you are using a glass thermometer, leave it in for 2 minutes. If you are using a digital thermometer, take it 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. If you are using a glass thermometer, leave it in for 4 to 5 minutes. If you are using a digital thermometer, take it 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). If you are using a glass thermometer, leave it in for 3 minutes. If you are using a digital thermometer, take it 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.