Best thermometer for babies: why I’d skip the in-ear one (and what to use instead)
Your baby feels hot. You grab the thermometer, get a number, and then wonder if you can even trust it. As a mum, I've been that worried parent. The best thermometer for a young baby is a simple digital one, used under the arm. The in-ear one most of us buy works better for older kids.
The short version
Best for babies: a digital thermometer under the arm
Skip for young babies: in-ear thermometers
Call 111 or go to ED if: your baby is floppy or hard to wake, has blue lips, is struggling to breathe, or has a rash that doesn't fade
What is the best thermometer for a baby?
A plain digital thermometer. It's accurate, easy to use, and usually the cheapest one on the shelf.
For babies and little ones under 5, pop it under their arm. Once your child is about 5 and can hold it still under their tongue, you can use it in their mouth instead.
It's not the flashiest option, I know. But when your baby is unwell, you want a number you can rely on. That's the one.
Why isn't an in-ear thermometer best for young babies?
If you've got an in-ear thermometer in the drawer, you haven't done anything wrong. They're quick, they look clever, and they work really well once kids are older. In a young baby, though, they're tricky to get right. Here's why.
That last one is the part I care about most. Picture this: your gut is telling you something's not right, but the thermometer says your baby's temperature is normal. It only takes one number like that to make you second-guess yourself.
So for a young baby, a simple digital underarm thermometer is the one I'd reach for. You don't need the expensive one.
Knowing when a temperature matters, and when it doesn't, is one of the things parents learn in the Sickness course. It helps you trust what you're seeing.
Have a look at our Sickness courseEar vs underarm vs forehead: which thermometer is most accurate?
There are so many thermometers out there, and the packaging all promises the same thing. Here's how they actually compare.
| Thermometer | Best for | What to know |
|---|---|---|
| Digital, under the arm | Babies and kids under 5 | Accurate, cheap and easy. Reads a little lower than inside the body, which is normal. |
| Digital, in the mouth | Kids 5 and over | The most accurate at home, once they can hold it under their tongue. |
| In-ear | Older kids | Quick and accurate when used right. Less reliable in young babies. |
| Forehead (infrared) | A quick check | Reads skin temperature, which changes with the room and blood flow. Double check with a digital one. |
| Forehead strips | Best to skip | Not accurate. |
| In the bottom (rectal) | Hospital only | Don't do this at home. You'll see overseas sites suggest it, but NZ advice is clear. |
| Old mercury glass | Best to skip | Toxic if it breaks. Swap it for a digital one. |
How do I take my baby's temperature under the arm?
Wriggly babies don't make this easy, so a cuddle is your best tool here.
- Turn the thermometer on.
- Tuck the tip into your baby's armpit, against their skin, not their clothes.
- Bring their arm down over it and hold them close. A cuddle keeps their arm in place.
- Leave it in for about 2 minutes, even if it beeps earlier. Some thermometers beep while they're still measuring.
- Take it out and read the number.
A little tip: if your baby has just come out of the bath or has been bundled up in layers, give them a few minutes first. Both can change the reading.
Top Thermometers Recommended by Parents
Vicks Fever Insight
WellCare Digital Thermometer Ultimate
The number is only one piece of the puzzle. In the Sickness course, you'll learn the signs to look for in your baby, so you know whether that number really matters.
Learn the signsWhy is the underarm reading lower?
An underarm reading is usually about half to 1 degree lower than the temperature inside your baby's body. That's normal. Your thermometer isn't broken.
You don't need to do any maths at 2am. When you see your GP, just tell them the number and that you took it under the arm. They'll know what that means.
What temperature is a fever in a baby?
A temperature of 38°C or higher is a fever. Normal is around 37°C.
If your baby is under 3 months and has a fever, get them checked by a doctor urgently, even if they seem okay. Little babies can hide how unwell they are.
For older babies, here's something I wish every parent knew: the number on its own doesn't tell you how sick your baby is. How they look and act tells you far more.
When should I get help?
It can be so hard to know whether you're overreacting. Here's a simple guide to help you decide.
And please hear this: you know your baby better than anyone. If your gut says something's wrong, listen to it, even if someone tells you it's probably nothing. As a paediatric nurse, I've seen what a difference it makes when parents trust that feeling and act on it.
Questions parents ask
Are ear thermometers accurate for newborns?
Not reliably. A newborn's ear is tiny, so the tip often doesn't fit or point at the eardrum properly. Even a little wax can make the reading too low. A digital thermometer under the arm is the one to use for young babies.
Are forehead thermometers good for babies?
They're quick, but they're not always accurate. They read the skin on the forehead, which changes with the room temperature and blood flow. If a forehead reading worries you or doesn't match how your baby seems, check it with a digital thermometer under the arm.
Why is the underarm reading lower than other methods?
Underarm readings are usually half to 1 degree lower than the temperature inside the body. That's expected. Just tell your GP that you measured under the arm, and they'll take it into account.
Do I need to check my baby's temperature if they seem fine?
No. If your baby is happy, feeding well and acting like themselves, there's no need to take their temperature. Check it if they feel hot or seem unwell.
Can I take my baby's temperature in their bottom?
Not at home. Rectal temperatures are sometimes taken in hospital, but NZ advice is not to do it at home. A digital thermometer under the arm is safe and accurate for babies.
Trust your instincts, and know what they're telling you
Imagine your baby spikes a fever at 2am. Instead of panic-Googling, you grab the right thermometer, check the signs, and know whether it's safe to manage at home or time to get help.
That's what knowing the signs gives you. Without them, it's easy to wait too long, or worry for nothing. No parent should have to guess in the moment that matters most.
Here's how to get there:
1Pick your course
2Learn the signs and what to do
3Feel confident when it matters
Find your courseNot ready yet? Start with the free CPR course
Paediatric nurse, mum, and trusted by 4,500+ NZ families. Charlotte has been a paediatric nurse for 12 years. She teaches parents how to trust their instincts and feel confident to act in emergencies, serious sickness and injuries.
This post is general information, not medical advice. If you're worried about your baby, see your GP, or call 111 in an emergency.