How to Take a Child’s Temperature: A Step-by-Step Guide
Quick Answer
Use a digital thermometer, never a mercury one. Which method to use depends on your child’s age, and the reading is only as good as the technique — so follow the instructions that came with your device. What the number means is a separate question from how to get the number right.
Start Here: Choose the Right Thermometer
Before you decide where to measure, decide what you are measuring with. Use a digital thermometer.
Do not use a mercury thermometer. These thin glass devices are filled with a silvery metal that is toxic. If one breaks, it can release harmful fumes. If you still have one at home, remove it rather than keep it as a spare.
Digital thermometers read the temperature at five different places on the body: the bottom (rectal), the mouth (oral), the forehead (temporal artery), the ear (tympanic), and the armpit (axillary).
Those five are not equally accurate, and that difference is the first thing worth knowing:
- Rectal — the most accurate
- Forehead — the next most accurate
- Oral and ear — accurate when done properly
- Armpit — the least accurate
Notice what that ranking does not say. Oral and ear readings are not second-rate methods; they are accurate when the technique is right. That is why the sections below spend as much time on how you measure as on what you measure with.
Whichever type you choose, follow the cleaning instructions on the package before the first use, and clean the device before and after every use afterward.
Which Method Fits Your Child’s Age
Not every method works at every age. Some devices need an ear canal, a mouth or a level of cooperation that a younger child simply does not have yet. Start from your child’s age and work backwards to the method.
| Method | Age it can be used |
|---|---|
| Rectal | Any age. Gives the best reading, and is the method to reach for with an infant under 3 months |
| Forehead | Any age |
| Ear | 6 months and older |
| Oral | 4 years and older |
| Armpit | Any age, as a quick screen — see the section further down |
The ear limit is the one parents most often work around, so it is worth knowing the reason behind it. An ear thermometer reads heat from the eardrum, and it needs to sit correctly inside the ear canal to do that. In babies younger than six months, the canal is too narrow for the device to sit properly, so the reading is not reliable.
Oral measurement starts at four years old. What the method asks of a child is worth picturing before you try it: holding the thermometer under one side of the tongue, lips sealed around it and teeth off it, for the whole measurement.
How to Take a Rectal Temperature
Rectal measurement gives the best reading, and it is the method to use with a baby under three months old.
Before you start. Put a small amount of lubricant, such as petroleum jelly, on the end of the thermometer and on your child’s bottom.
Position your child. Either belly down across your lap or on a firm surface, or on their back with their legs pulled up toward the chest. Both work — pick the one that lets you hold your child still.
Insert gently. Turn the thermometer on and slide it in gently. There should not be any resistance. If you feel resistance, stop rather than push against it. For how far to go, follow the instructions that came with your thermometer.
Hold and read. Keep your child still and follow the thermometer’s instructions for when to remove it, then read the display.
Afterwards. Label this thermometer clearly as the rectal one. A multi-use digital thermometer can measure rectally, orally or under the arm — which is exactly why it should never travel between the bottom and the mouth. If you keep both a rectal and an oral thermometer, label both.
How to Take an Oral Temperature
Oral measurement starts at four years old. Before you begin, if your child has just had something hot or cold to drink, wait 30 minutes.
Place the thermometer. Put the tip under one side of the tongue, toward the back of the mouth.
Keep it in place. Your child should hold the thermometer with their lips and fingers, not their teeth. Keep the lips closed around the thermometer and follow the device instructions for when to remove it.
How to Take a Forehead Temperature
Forehead thermometers can be used at any age. Because models work differently, follow the instructions that came with your device for exactly how and where to place or move the sensor.
Before you measure. Direct sunlight can affect a forehead reading, and so can recent exposure to cold.
Take the reading. Aim or slide the sensor as the device instructions describe, then read the display.
How to Take an Ear Temperature
Ear thermometers can be used from six months of age. Follow the instructions that came with your device, because correct placement in the ear canal matters for an accurate reading.
Position the ear. Pull the ear back. If your child is over one year old, pull it back and up. Then aim the tip of the thermometer between the opposite eye and ear.
After cold exposure. If your child has just come inside from the cold, wait 15 minutes indoors before taking an ear reading.
Take the reading. Hold the position until the measurement is done, then read the display.
What About Armpit, Pacifier, and Forehead Strip Thermometers?
Some methods are less accurate than the ones described above. They can still be useful for a quick screen, as long as you know what you are getting.
Armpit. An armpit temperature can be used at any age as a quick screen. It is the least accurate of the measurement methods described above, so follow the instructions that came with your thermometer and treat the result as a screening reading.
Pacifier thermometers. These are less accurate than digital rectal, forehead, ear, or oral measurement.
Forehead fever strips. These strips are also less accurate and are best treated as a quick screening method rather than a substitute for a digital thermometer.
Common Myth
“If I own a thermometer, I can use it the same way for any child.”
The device is only half of it — the method has to match the age. Ear thermometers are used from six months, and oral measurement starts at four years. Check the method against your child’s age before you start.
What to Do Once You Have a Reading
Before you move on, record three things: the temperature you saw on the display, where you measured it, and when you took the reading.
Those details give you a clear record of the measurement you actually took. If you need help understanding what the reading means or what to do next, see our guide to fever in children.
Quick Checklist: Did You Measure Correctly?
- Did you choose a method that fits your child’s age?
- Did you follow the instructions that came with your thermometer?
- If you used an oral thermometer, did you wait 30 minutes after a hot or cold drink?
- If you used an oral thermometer, did your child hold it with their lips, not their teeth?
- If you used an ear thermometer, did you pull the ear back — and back and up if your child is over one year old?
- If you used an ear thermometer after being outside in the cold, did you wait 15 minutes indoors?
- If you used a forehead thermometer, was your child out of direct sunlight?
- If you used a rectal thermometer, did you stop if you felt any resistance?
- Did you clean the thermometer according to the device instructions?
FHG Science Note
Different measurement sites are not equally accurate. That is why choosing the right method and using the technique correctly both matter when you take a child’s temperature.
Sources
- American Academy of Pediatrics / HealthyChildren.org — How to Take Your Child’s Temperature. Updated April 17, 2024.
This article provides general parent education based on the cited AAP source. It explains how to measure a child’s temperature and does not interpret a reading, diagnose an illness, or provide medication dosing. It is not a substitute for advice from your child’s healthcare provider. If your child has severe, unusual or worsening symptoms, contact a healthcare professional.
