How to Measure a Temperature

Taking a Child's Temperature

Getting an accurate measurement of your child's temperature requires some practice. If you have questions about these procedures, ask your health care provider to show you how it's done. Then ask them to watch you do it.

Where to Take the Temperature

Temperatures measured rectally are the most accurate. Temperatures measured orally, by electronic pacifier, or by ear canal are also accurate if done properly. Temperatures measured in the armpit are the least accurate, but they are better than no measurement.

• An infant less than 3 months old (90 days old):

  An armpit temperature is preferred for reasons of safety and is adequate for screening. If the armpit temperature is over 99°F (or 37.2°C), check it with a rectal temperature. The reason you need to take a rectal temperature for young infants is that if they have a true fever, they need to be seen immediately.

• A child less than 4 or 5 years old:

  A rectal or electronic pacifier temperature is preferred. An ear temperature is fine after 6 months old. An axillary (armpit) temperature is adequate for screening if it is taken correctly.

• A child more than 4 or 5 years old:

  Take the temperature orally (by mouth).

How to Take Rectal Temperatures

1. If you are using a glass thermometer, shake until the mercury line is below 99°F (37.2°C). If you are using a digital thermometer, turn it on.
2. Have your child lie stomach down on your lap.
3. Before you insert the thermometer, put some petroleum jelly on the end of the thermometer and on the opening of the anus.
4. Insert the thermometer gently into the rectum about 1 inch. During the first 6 months of life, gently insert the rectal thermometer 1/4 to 1/2 inch (inserting until the silver tip disappears is about 1/2 inch). Never try to force it past any resistance. Forcing could damage the bowel.
5. Hold your child still while the thermometer is in.
6. If you are using a glass thermometer, leave it in your child's rectum for 2 minutes before you take it out. If you are using a digital thermometer, take it out when you hear the correct signal (usually a series of beeps).
7. Read the temperature on the thermometer. If you are using a glass thermometer, you may have to rotate the thermometer until you can see the end of the mercury line.
8. Fever is a rectal temperature over 100.4°F, or 38°C.

How to Take Armpit (Axillary) Temperatures

1. If you are using a glass thermometer, shake it until the mercury line is below 98.6°F (37°C).
2. Place the tip of the thermometer in a dry armpit.
3. Close the armpit by holding the elbow against the chest for 4 or 5 minutes. You may miss detecting a fever if the glass thermometer is removed before 4 minutes.
4. After 4 or 5 minutes take the glass thermometer out and read the temperature by finding where the mercury line ends. You may need to rotate the thermometer until you can see the mercury. If you are using a digital thermometer, remove it after you hear the signal (usually a series of beeps) and read the temperature on the screen.
5. If you're uncertain about the result, check it by taking a rectal temperature.
6. Fever is an armpit temperature over 99°F, or 37.2°C.

How to Take Oral Temperatures

1. Be sure your child has not had a cold or hot drink in the last 30 minutes.
2. If you are using a glass thermometer, shake the thermometer until the mercury line is below 98.6°F (37°C). If you are using a digital thermometer, turn it on.
3. Place the tip of the thermometer under one side of the tongue and toward the back. An accurate temperature depends on proper placement. Ask your health care provider to show you where it should go.
4. Have your child hold the thermometer in place with his lips and fingers (not his teeth). He should breathe through his nose, keeping his mouth closed. If your child can't keep his mouth closed because his nose is blocked, suction out the nose.
5. Leave the glass thermometer in the mouth for 3 minutes. Leave a digital thermometer in the mouth until you hear the correct signal (usually a series of beeps).
6. Read the temperature. If you are using a glass thermometer, you may need to rotate the thermometer until you can see where the mercury line ends.
7. Fever is an oral temperature over 99.5°F, or 37.5°C.

Types of Thermometers

1. Glass (with mercury) thermometers

   This type of thermometer has been around since 1870. These are the least expensive thermometers. They have some disadvantages. They measure temperatures slowly and are often hard to read. If broken, they cause a mercury spill which can be harmful and difficult to clean up. The American Academy of Pediatrics urges parents not to use mercury thermometers.

   Glass thermometers come in two forms, oral with a thin tip and rectal with a rounder tip. This difference is not too important. If necessary, a rectal thermometer can be used in the mouth as long as the thermometer is cleaned with rubbing alcohol. An oral thermometer can be used in the rectum if you are extra careful when you put it in.

2. Digital electronic thermometers

   Digital electronic thermometers measure temperatures with a heat sensor and require a button battery. They measure temperatures quickly, usually in less than 30 seconds. The temperature is displayed in numbers on a small screen. The same thermometer can be used to take both rectal and oral temperatures.

   A study in Consumer Reports magazine (January 1988) found that digital thermometers were more accurate than glass thermometers. Buy one for your family; they cost about $10.00.

3. Ear thermometers

   Many hospitals and medical offices now take your child's temperature using an infrared thermometer that reads the temperature of the eardrum. In general, the eardrum temperature provides a measurement that is as accurate as the rectal temperature.

   The biggest advantage of this thermometer is that it measures temperatures in less than 2 seconds. It also does not require cooperation by the child and does not cause any discomfort. Ear thermometers for use at home have been developed, but they are expensive.

4. Digital electronic pacifier thermometers

   The new electronic pacifier thermometers have a heat sensor and are powered by a button battery. These pacifiers let you measure oral temperature in younger children. They are quite accurate if 0.5°F is added to the digital reading. They take approximately 3 minutes to reach a steady state. An added advantage is their lower cost of $15.

5. Temperature strips

   Liquid crystal strips put on the forehead have been studied and have been found to be inaccurate. They do not detect an elevated temperature in most children with fever.

   Touching the forehead is somewhat reliable for detecting fevers over 102°F (38.9°C) but tends to miss mild fevers.

Conversion of Degrees Fahrenheit (F) to Degrees Celsius (C)

Temperatures can be measured in degrees Fahrenheit (F) or degrees Celsius (C). The table below shows the temperatures in degrees Celsius that are equivalent to temperatures measured in degrees Fahrenheit:

 
              98.6 degrees F  =  37   degrees C 
              99   degrees F  =  37.2 degrees C 
              99.5 degrees F  =  37.5 degrees C 
              99   degrees F  =  37.2 degrees C 
             100   degrees F  =  37.8 degrees C 
             100.4 degrees F  =  38   degrees C 
             101   degrees F  =  38.3 degrees C 
             102   degrees F  =  38.9 degrees C 
             103   degrees F  =  39.5 degrees C 
             104   degrees F  =  40   degrees C 
             105   degrees F  =  40.6 degrees C 
             106   degrees F  =  41.1 degrees C 
             107   degrees F  =  41.7 degrees C