Best baby thermometer: which type to choose
It's one of those objects you hope you'll never use and yet, sooner or later, you'll need it: the thermometer. The first fever always arrives at the least convenient moment — at night, on the weekend, when the pediatrician's office is closed. Having a reliable, easy-to-use thermometer at home lets you face that moment calmly. Here is which type to choose, following what the American Academy of Pediatrics and the NHS say.
Which thermometer is most accurate, and which most convenient
The AAP ranks the methods clearly: rectal temperatures are the most accurate, forehead temperatures are the next most accurate, oral and ear temperatures are accurate if done properly, and armpit temperatures are the least accurate, though they can be used to screen a child of any age. A rectal reading gives the best result especially for infants under 3 months.
The forehead (temporal artery) thermometer reads the infrared heat coming off the blood vessel that runs across the forehead just below the skin. It can be used at any age, it is quick, and non-contact models let you check a sleeping baby without waking them and may help reduce the risk of passing germs. That is why many families keep one for everyday checks and a digital multi-use thermometer for a rectal reading when it counts. Search for forehead thermometers on Amazon
What to look for when you choose one: a clear display you can read at night, a memory of past readings to tell the doctor how the fever has gone, and instructions that state exactly how far from the forehead to hold it and how to aim or slide it — accuracy depends on following them.
The types of baby thermometer compared
Digital multi-use thermometer (rectal, oral, armpit)
Measures temperature in the bottom, the mouth or the armpit when the tip touches the skin. The AAP does not recommend oral use until age 4, and advises labelling the thermometer “rectal” so it is never used in the mouth. For a rectal reading in babies under 6 months, the tip goes in about 1/2 inch, gently, with a little petroleum jelly, and stays until it beeps. In the UK, the NHS describes taking a child's temperature under the armpit with a digital thermometer.
Forehead (temporal artery) thermometer
Usable at any age; contact and non-contact models exist. Direct sunlight and cold temperatures after being outside can affect the reading.
Ear (tympanic) thermometer
Reads infrared heat from the eardrum. For children 6 months and older: it is not reliable for younger babies, whose ear canals are too narrow, and it needs to be placed correctly in the ear canal to be accurate.
Forehead strip or pacifier thermometer
A convenient idea, but the AAP lists both among the less accurate ways of checking for fever: fine for a quick screen, not for deciding what to do next.
| Thermometer type | Accuracy (AAP) | Age | When to use it |
|---|---|---|---|
| Digital, rectal | Most accurate | Any age; best reading under 3 months | When the number matters |
| Forehead (temporal artery) | Next most accurate | Any age | Everyday checks, even while the baby sleeps |
| Ear (tympanic) | Accurate if placed properly | 6 months and older | Older babies and toddlers |
| Digital, armpit | Least accurate | Any age | Screening |
| Strip or pacifier | Less accurate | Pacifier: 1 year and younger | Quick screening only |
How to take a baby's temperature correctly
- Follow the instructions for your model. The AAP's first rule for any digital thermometer: how close to hold it, where to aim it and how long to wait are specific to the device.
- Wait after a bath or blankets. The NHS notes that a child's temperature may be higher for a short time after a bath or being wrapped in a blanket: wait a few minutes and try again.
- Wait after coming in from the cold. Cold temperatures after being outside can affect forehead and ear readings; for ear readings the AAP suggests waiting 15 minutes indoors.
- Keep it clean. Clean the thermometer as the package says before and after use, and keep the rectal one for rectal use only.
When a baby's temperature counts as a fever (and when to call the doctor)
The AAP defines a fever as 100.4 °F (38 °C) or higher; the NHS also calls 38 °C or more a high temperature. The AAP says to call your child's doctor right away if your child has a fever and:
- is younger than 3 months (12 weeks) with a temperature of 100.4 °F (38 °C) or higher;
- has a temperature that rises above 104 °F (40 °C) repeatedly, at any age;
- looks very ill, is unusually drowsy or is very fussy;
- has other symptoms such as a stiff neck, breathing difficulty, an unexplained rash, or repeated vomiting or diarrhea;
- has had a seizure, or has immune system problems.
Call as well if the fever lasts more than 24 hours in a child younger than 2. In the UK, the NHS says to call 111 if a baby under 3 months has a temperature of 38 °C or higher, a baby of 3 to 6 months has 39 °C or higher, or a high temperature has lasted 5 days or more — and to call 999 for signs such as a rash that does not fade under a glass, a stiff neck, or difficulty breathing.
Important: the thermometer measures, it doesn't treat. Don't give any fever medicine to a baby without checking with your pediatrician or pharmacist first, especially in the first months.
Choosing a baby thermometer in short
A digital multi-use thermometer for a rectal reading when it matters, and a forehead thermometer for quick checks, cover the first year. Follow the instructions for your model, and remember the rule of the first 3 months: a temperature of 100.4 °F (38 °C) or higher means calling the doctor right away.
It's also the only measuring device in that small first-months kit: everything else is daily care, from the newborn skin-care routine to the barrier cream you'll be glad to have at the first sign of diaper rash.
Frequently asked questions about baby thermometers
What is the best thermometer for a newborn?
A digital one — the American Academy of Pediatrics says to use a digital thermometer and never a mercury one. A digital multi-use thermometer used rectally gives the most accurate reading, especially under 3 months. A forehead (temporal artery) thermometer is the next most accurate, can be used at any age and is the most convenient for quick checks, so many families keep both.
Are forehead infrared thermometers reliable?
According to the AAP, forehead temperatures are the next most accurate after rectal ones, and temporal artery thermometers can be used on children of any age. Accuracy depends on following the instructions for that model: how close to hold it and how to aim or slide it. Direct sunlight and cold temperatures after being outside can affect the reading.
Is an ear (tympanic) thermometer good for a newborn?
Not in the first months. The AAP says ear thermometers can be used on children 6 months and older, and are not reliable for younger babies, whose ear canals are too narrow.
Are forehead strips or pacifier thermometers reliable?
Not very. The AAP lists fever strips and pacifier thermometers among the less accurate ways of checking for fever: fine for quick screening, but they do not work as well as a digital thermometer used rectally, on the forehead, in the ear or by mouth.
What temperature counts as a fever in a baby?
The AAP defines a fever as a temperature of 100.4 °F (38 °C) or higher; the NHS also calls 38 °C or more a high temperature.
When should you call the doctor right away for a fever?
The AAP says to call right away if a baby younger than 3 months (12 weeks) has a temperature of 100.4 °F (38 °C) or higher, if the temperature rises above 104 °F (40 °C) repeatedly at any age, or if the child looks very ill, is unusually drowsy or very fussy, has a stiff neck, breathing difficulty, an unexplained rash, repeated vomiting or diarrhea, or has had a seizure. In the UK, the NHS says to call 111 if a baby under 3 months has 38 °C or higher, or a baby of 3 to 6 months has 39 °C or higher.
Sources
- American Academy of Pediatrics, HealthyChildren.org — How to Take Your Child's Temperature (last updated April 17, 2024; accessed September 26, 2026). Source for: digital, never mercury; the accuracy ranking of rectal, forehead, ear, oral and armpit readings; forehead thermometers at any age, ear thermometers from 6 months; strips and pacifier thermometers as less accurate; fever at 100.4 °F (38 °C).
- American Academy of Pediatrics, HealthyChildren.org — When to Call the Pediatrician: Fever (last updated December 2, 2022; accessed September 26, 2026). Source for: when to call right away, including under 3 months at 100.4 °F (38 °C) and above 104 °F (40 °C) repeatedly, and a fever lasting more than 24 hours under age 2.
- NHS — High temperature (fever) in children (page last reviewed January 3, 2024; accessed September 26, 2026). Source for: 38 °C or more as a high temperature, the armpit method, higher readings after a bath or blankets, when to call 111 and 999.