How to Measure a Fever

mom and child with fever

Before you can treat a fever it is important to accurately measure your child’s temperature. Here are a few easy techniques to get you started.

When a child is sick, the first thing the doctor’s office may ask is, “What’s her temperature and how did you take it?” There are a variety of thermometers and ways to take a child’s temperature, so it’s helpful to know what’s recommended for each age.

Basic digital thermometers are a good choice. They are accurate, fast, easy to use, inexpensive, and can be used for a variety of temperature-taking methods: in the bottom (rectal), by mouth (oral), or under the arm.

NOTE: A thermometer used for taking temperatures should not be used for other methods.

Babies under age 3 months

The rectal method is the most reliable for young infants. If your baby is under 3 months of age and has a temperature of 100.4°F or higher, contact your doctor right away. Babies this young need to be checked for infection or disease.

To take an rectal temperature:

  • Wash the thermometer, then rinse with cool water
  • Coat the tip with petroleum jelly
  • Place your child either on his back with knees bent or on his belly.
  • Holding your child still, insert the thermometer ½ to 1 inch into the bottom
  • Hold until it beeps, then remove for reading

Children under age 4 years

Active, older children may not cooperate well with the rectal method. Another option is the underarm method, but it is less accurate. An underarm reading can be as much as 2 degrees lower than an internal rectal reading.

To take an underarm temperature:

  • Remove your child’s shirt
  • Make sure the underarm is dry
  • Press the thermometer tip against the armpit
  • Keep your child’s arm firmly against her side
  • Hold until it beeps, then remove for reading

Children ages 4 & up

For older kids, a temperature taken by mouth is accurate when taken properly (your child must be able to hold the thermometer in place long enough to get a reading).

To take an oral temperature:

  • Wash the thermometer, then rinse with cool water
  • Put the tip under your child’s tongue, near the back of the mouth
  • Hold in place until it beeps, then remove for reading

Other ways to take your child’s temperature

  • Ear thermometers are quick and comfortable, but can be tricky to use
  • Temporal artery thermometers are swiped across the forehead (they may be reliable, but are more expensive)
  • Fever strips and pacifier thermometers are not recommended by the American Academy of Pediatrics.

Fevers could be a sign that your child’s body is fighting off an infection. Most fevers are caused by common childhood illnesses like colds, flu, ear infections, bronchitis, and tonsillitis. Usually, a fever is just a symptom of an infection or other condition. In most cases, a fever will go away on its own in 2 or 3 days.

If you have questions or concerns, talk to your doctor.