Everything You Need to Know About Thermometers

By |
Everything You Need to Know About Thermometers
George Rudy

When it comes to your health, taking your body's temperature can have a variety of applications. Usually, you want to know if you or a loved one is running a fever, but thermometers are also valuable tools for monitoring illness and family planning.

The toxicity of mercury thermometers led to a rise in digital and infrared thermometers with extremely competitive features. Digital thermometers use heat sensors to measure oral, axillary (underarm), and rectal temperatures while infrared models use infrared technology to measure in-ear or temporal (forehead) temperatures.

Body temperatures for the same person vary depending on where you measure them. In-ear and rectal temperature readings are higher than oral readings while under arm and forehead readings are cooler. This means that a rectal temperature could be a full 2°F higher than an armpit reading.

Please note that, in order to get accurate oral readings, you should wait 15 minutes after eating or drinking anything.

For further guidance on temperature variations and to see which test position is age-appropriate for your kids, see the table below. Though rectal readings are the most accurate, we used oral readings as our baseline since it's the most common test position.

"You should also consider how invasive you want your thermometer to be, especially when taking care of sick kids."

Pacifier thermometers, though increasingly popular, are not currently recommended by the American Academy of Pediatrics (AAP). The AAP doesn't believe there's enough evidence to support the reliability of these thermometers, so they were omitted from our analysis. Based on several studies and the Mayo Clinic's endorsement, we did, however, include forehead thermometers for use on newborns and toddlers alike.

Now that you know who can use which thermometer, how do you tell the great ones apart from the duds? It all comes down to what features you value and how many people's temperatures you need to take.

Olivia Geyelin

Infrared thermometers offer the fastest results (at a price), but speedy readings on regular digital readings are usually predictive. While these readings provide accurate guesses, actual body temperature takes longer than a few seconds to record. Temperature recall can help prevent frequent measurements in the heat of the moment, which are often inaccurate because most thermometers require 30–60 seconds to cool down.

Backlit screens can either be blindingly bright or make nighttime measurements a breeze. Loud, signaling beeps stir children and aggravate headaches, but complete silence turns a self-reading into a nearly impossible feat. You should also consider how invasive you want your thermometer to be, especially when taking care of sick kids.

The most common feature that can make or break any thermometer is battery life. You can stock up on obscure or standard batteries, or maybe you don't want to deal with batteries at all.


If you're interested in thermometers beyond the scope of the common cold, there are other features you want to consider. App connectivity can store your symptom history and tether your temperature to a comprehensive health journal which can be useful to doctors or for your personal medical history.

If you are looking for a thermometer to help with family planning, you need a basal body thermometer (BBT). This kind of thermometer should measure temperature to the 1/100th of a degree in order to track the subtle temperature changes of an ovulation window. When choosing a BBT, a longer read time is preferred to ensure the high level of accuracy these measurements require.

How We Chose Our Picks

olivia geyelin

Taking all these factors into consideration, we went to bat for your family. We delved into medical journals and associations' recommendations to find out what the safest options were for your family. Armed with that knowledge, we cross-referenced professional reviews from The Sweethome, Consumer Reports, and Best Reviews with user reviews from Amazon, Target, Walmart, and major pharmacy chains. After we could see again, we tested our picks against a Welch Allyn SureTemp Plus 690 thermometer at a doctor's office. We were then able to determine which thermometer would be the most reliable for your physical (and emotional) needs.

Note: If using a thermometer rectally, label it as such and clean it thoroughly between uses. In general, regardless of a thermometer's level of waterproofing, do not boil any of these thermometers to sterilize them. These aren't your grandmother's thermometers; rubbing alcohol or antibacterial soap and water will work just fine.

At Gizmos, we find products that help you thrive.

When you use our links, we may earn a commission, but it will never cost you extra or impact our recommendations.

Learn More

The Gizmos Team