How to Take Your Child's Temperature Accurately

Why the method matters as much as the number

When your child feels warm, it is tempting to focus only on the number on the display. But where and how you take the temperature changes that number, sometimes by a full degree or more. A rectal reading tends to reflect core body temperature most closely, while an armpit reading usually runs lower and a poorly aimed ear or forehead reading can read higher or lower than the truth. That is why your pediatrician will often ask not just what the temperature was, but how you took it. Knowing the method behind the number lets everyone interpret it correctly, especially for babies, where an accurate reading can change what happens next.

The main types of thermometers

Modern digital thermometers are inexpensive, fast, and safe. The American Academy of Pediatrics (AAP) recommends digital multiuse thermometers and advises against old glass mercury thermometers, which can break and release toxic mercury. The common options measure at different body sites:

• Rectal (bottom): generally the most accurate way to measure core temperature in infants and young children, which is why it is the standard for babies.
• Oral (mouth): reliable once a child is old enough to hold the tip under the tongue with lips closed, generally around age 4 to 5.
• Axillary (armpit): quick and easy, but the least precise; it usually reads lower than core temperature and is best used as a screen.
• Tympanic (ear): a fast infrared reading, but the ear canal shape, earwax, and positioning can affect accuracy; not recommended for babies under 6 months.
• Temporal artery (forehead): an infrared scanner swept across or aimed at the forehead; convenient and improving, though technique and skin conditions can affect the result.

Two products to skip: pacifier thermometers and forehead strip thermometers are not considered reliable and should not be used to make decisions about a fever.

Which method to use, by age

The best method depends mostly on your child's age and ability to cooperate. AAP guidance can be summarized this way:

• Birth to 3 months: use a rectal thermometer for an accurate reading. An armpit reading can be a first check, but any elevated result should be confirmed rectally, and a fever in this age group needs prompt medical attention.
• 3 months to about 4 years: rectal remains the most accurate. A temporal artery (forehead) thermometer is a reasonable choice, and a tympanic (ear) thermometer can be used after 6 months. Armpit readings work for screening.
• 4 years and older: an oral reading is convenient and accurate once your child can keep the thermometer under the tongue with the mouth closed. Forehead, ear, and armpit methods are still fine.

How to take an accurate reading

Whatever method you use, start with a clean digital thermometer and read the manufacturer's instructions, since scanners vary. Wash the tip with soap and water or wipe it with rubbing alcohol before and after use. For oral readings, wait about 15 minutes after your child has had a hot or cold drink or food. Here is how to handle each site:

• Rectal: lay your baby on their back or tummy, put a small amount of petroleum jelly on the tip, and gently insert it no more than about a half-inch (roughly one centimeter) in a young infant, never forcing it, until it feels just snug. Hold it in place and keep your baby still until it beeps, then remove and read. Keep one thermometer labeled for rectal use only.
• Oral: place the tip under the tongue toward the back, have your child close their lips, and wait for the beep without biting down or talking.
• Axillary: place the tip in the center of a dry armpit against bare skin, then hold the arm snugly against the body until it beeps.
• Tympanic: straighten the ear canal by following the device's age-specific positioning instructions, since the recommended direction differs for infants and older children, then aim as directed and wait for the reading.
• Temporal: follow the device's instructions for swiping across or aiming at the forehead, and keep the area free of sweat, hair, hats, and direct sun or cold.

For a baby in the first few months of life, a fever is treated as urgent, so measure rectally and call your pediatrician or seek care right away rather than waiting to see how things go. Always write down the temperature, the time, and the method you used, and never use a glass mercury thermometer. Our fever management guide lists the emergency warning signs that mean your child should be seen regardless of the exact number.

Common mistakes that skew a reading

Most inaccurate readings come from technique, not a broken device. Watch for these:

• Taking an oral temperature too soon after eating or drinking something hot or cold.
• Not holding the arm tightly enough for an armpit reading, so air cools the tip.
• Aiming an ear thermometer at the canal wall or measuring through earwax or an ear infection.
• Scanning a forehead covered by sweat, hair, or a hat, or right after coming in from the cold.
• Comparing readings taken by different methods as if they were the same, or using an unreliable pacifier or strip thermometer.

When a reading should prompt a call

There is no single temperature that means the same thing for every child. What counts as a fever, and the reading that should prompt a call, depends heavily on your child's age, with stricter guidance for young infants than for older children. Rather than repeat those age-specific numbers here, see our fever management guide, which explains when a given reading warrants a call to your pediatrician or a trip to urgent care. When you do call, share the actual number and the method you used.

• Your child is younger than about three months and feels warm or has any measured fever, which always warrants a prompt call.
• The fever keeps returning or lasts longer than your pediatrician's guidance for your child's age.
• You are worried about how your child looks or acts, or you are unsure whether a reading counts as a fever; our fever management guide covers the illness and emergency warning signs to watch for.

Choosing and caring for your thermometer

A basic digital thermometer that can be used at more than one site is all most families need. Keep a separate, clearly labeled one for rectal use so it is never confused with the oral thermometer. Clean it before and after each use, replace the batteries when readings become slow or inconsistent, and store it where you can find it quickly. If you want to move between Celsius and Fahrenheit, or check the conversion your pediatrician quotes over the phone, use our temperature converter. Any medication guidance, including fever reducers, should come from your clinician or pharmacist, who will confirm the right choice and dose for your child.