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Having a reliable medical thermometer at home can be incredibly helpful. The ability to accurately find out if someone has a fever gives you much-needed information about important next steps for their care.

There are many types of contact and contact-free thermometers to choose from. The ages of your household members, as well as personal preference, can help you determine which types to buy.

Like any other device in your home, it’s important to understand how your thermometer works. Not every type works the same way or is designed to provide the same temperature readings.

Guesswork is the last thing you want to rely on when someone is sick. Here’s an overview of medical thermometers, how to use them, and what their measurements mean.

No matter which type you choose, read the manufacturer’s instructions carefully. No thermometer will provide accurate results if it’s used incorrectly.

Never use a thermometer on a person that is meant for another purpose, such as a laboratory or meat thermometer. These won’t provide accurate readings.

If you’re a parent, you may be wondering why we’re omitting forehead strip thermometers from this roundup. Strip thermometers are inexpensive and quick to use. However, since they measure skin temperature rather than body temperature, they’re significantly less accurate and should be avoided.

Digital thermometer

types of thermometers

Digital thermometers work by using heat sensors that determine body temperature.

They can be used to take temperature readings in the mouth, rectum, or armpit.

When assessing digital thermometer readings, keep in mind that armpit (axillary) temperature runs about ½ to 1°F (0.6°C) cooler than oral readings. Rectal thermometers run ½ to 1°F (0.6°C) warmer than oral readings.


Digital thermometers provide accurate readings in about 1 minute or less.


In order to get an accurate reading from oral use, the tip of the device must be placed under the tongue with the mouth completely closed. For this reason, rectal readings are considered to be the most accurate for infants and small children. Additionally:

  • Oral readings won’t be accurate if they are taken too close to eating or drinking, because results may be skewed by your food or drink’s temperature. Wait at least 15 minutes.
  • Rectal readings may be uncomfortable to get for infants and small children.
  • You shouldn’t use the same thermometer for both rectal and oral readings. This may require the purchase of two thermometers, which should be labeled.
  • Batteries in thermometers should be replaced periodically. Make sure you have the right type of batteries on hand for your device and that you understand how to change them, so you’re not left scrambling in an emergency.

Oral thermometer

types of thermometers

Oral temperature can be taken by either a digital or mercury thermometer. We’ll go over the benefits and drawbacks of mercury thermometers below.

The average oral temperature reading is 98.6°F (37°C). However, any oral temperature from 97°F (36.1°C) to 99°F (37.2°C) is considered typical. Some people run naturally cool, and others slightly warmer. It’s a good idea to know what your temperature typically is so you can assess whether you’re running a fever when you feel sick.


Oral thermometers are most accurate in children over 3 and in adults.


Small children and people with breathing issues may not be able to keep their mouths closed long enough to acquire an accurate reading.

Digital ear (tympanic) thermometer

types of thermometers

Tympanic thermometers measure the temperature inside the ear canal through infrared ray technology.

Tympanic readings are 0.5°F (0.3°C) to 1°F (0.6°C) higher than oral temperature readings.


Tympanic thermometers provide fast and accurate readings and may be preferable to oral or rectal thermometers, especially in children.


  • Due to the size of the ear canal, tympanic thermometers aren’t recommended for infants under 6 months old.
  • They must be positioned properly in order to get accurate results.
  • Obstructions like earwax may skew results.
  • They may not fit properly in a small or curved ear canal.

Forehead (temporal) thermometer

types of thermometers

Forehead thermometers use infrared sensors to measure the temperature of the superficial temporal artery, which is a branch of the carotid artery.

Some are known as non-contact infrared thermometers.

Forehead thermometers that require no physical contact have become very popular for use in venues such as airports, stores, and stadiums.

Forehead temperature readings run around 1°F (0.6°C) cooler than oral temperature readings.


  • Temporal thermometers provide quick readings, within several seconds.
  • They are easily administered and can be used on infants, children, and adults.
  • Some research indicates that temporal thermometers may be as accurate as rectal thermometers in children, and provide better readings than ear or armpit thermometers can. However, these findings aren’t conclusive and have been disputed in other studies.


  • Forehead thermometers must be positioned accurately and according to the manufacturer’s instructions, or they will not provide the right reading.
  • Readings can be affected by external factors, including drafts, wind, indoor heating, and direct sunlight.
  • Wearing certain clothing, such as hats or heavy coats, can skew the results.

App-based thermometer

types of thermometers

Most free phone apps designed to take temperature readings are meant for recording the temperature of environments, not people.

Phone apps that help with taking people’s temperatures rely on digital thermometers that link back to the app via Bluetooth connection.


  • Temperatures can be taken orally, rectally, or under the arm.
  • They provide readings within 8 to 10 seconds.
  • Some apps let you upload your anonymous temperature readings to a health and weather map, which can help make local authorities aware of illness spikes in your geographic area.
  • Some apps provide suggestions for medical next steps, based on the reading.
  • Most apps provide you with the ability to keep a log of multiple people’s temperatures.


  • Not every app or thermometer that connects to an app is reliable. Some manufacturers have better track records than others.
  • App-based thermometers may be significantly more expensive than digital thermometers without Bluetooth connectivity.

Pacifier thermometer

types of thermometers

If your baby uses a pacifier, this may be an easy way for you to record their approximate temperature.


Ease of use is the biggest benefit of pacifier thermometers.


Pacifier thermometers must remain in the mouth, without moving, for up to 6 minutes. Additionally, they provide an approximation of temperature rather than an exact reading.

Mercury (liquid in glass) thermometer

types of thermometers

Mercury thermometers were once the only option available for taking temperature.

Due to safety concerns, they’re no longer widely available and may even be illegal where you live.


  • Mercury thermometers provide accurate temperature readings and can be used orally, rectally, or under the arm.
  • They don’t require batteries.


  • Since they’re made from glass, mercury thermometers may break easily, allowing toxic mercury to escape.
  • They may also cause cuts or glass splinters if they break.
  • Since they contain a hazardous substance, mercury thermometers must be disposed of properly and can’t be thrown into the trash.
  • They can be hard to read and must stay in place for 3 minutes.

The best thermometer is the one that you can use most comfortably and correctly. It’s also helpful if your thermometer comes from a reliable manufacturer.

Rectal thermometers are still considered by many medical professionals to be the gold standard for babies and children. However, oral and forehead readings are also typically very reliable in these age groups.

Always keep in mind that temperature readings vary, based on how the thermometer is administered:

  • Rectal thermometer readings will be around 0.5°F (0.3°C) to 1°F (0.6°C) higher than oral temperature readings.
  • Tympanic thermometer readings are typically 0.5°F (0.3°C) to 1°F (0.6°C) higher than oral temperature readings.
  • Axillary thermometer readings can be 0.5°F (0.3°C) to 1°F (0.6°C) lower than oral temperature readings (and may be the least reliable).
  • Temporal thermometer readings are often 0.5°F (0.3°C) to 1°F (0.6°C) lower than oral temperature readings.

To take temperature orally with a digital thermometer:

  1. Wash your hands.
  2. Make sure your thermometer is clean and has working batteries.
  3. Turn the thermometer on. Slip the plastic sheath over the bottom tip of the thermometer.
  4. The thermometer will indicate that it’s ready to be used with a sound, light, or both.
  5. Place the thermometer’s tip underneath the tongue. Some thermometers come with grooves that indicate how far into the mouth it should go.
  6. Keep your mouth closed until you hear a beep or similar type of sound.
  7. Remove the thermometer and read it.
  8. Rewash your hands.
  9. Clean the thermometer between uses according to the manufacturer’s directions, even if only one person is using it.

To take someone’s temperature rectally with a digital thermometer:

  1. Wash your hands.
  2. Make sure your thermometer is clean and has working batteries.
  3. Cover the tip of the thermometer with a plastic sheath and apply lubricant, such as petroleum jelly or a water-based lubricant such as K-Y jelly.
  4. Babies can be placed on their backs, with their legs in the air. Children and adults may be more comfortable lying on their stomachs.
  5. Turn the thermometer on and wait for it to tell you it’s ready.
  6. Keeping the thermometer straight, gently insert the tip of the thermometer into the rectum, no more than 1 inch.
  7. Hold it in place so it doesn’t slip out.
  8. Wait to hear a beep or similar sound.
  9. Remove the thermometer and read it.
  10. Clean the thermometer according to the manufacturer’s directions before storing or reusing.
  11. Rewash your hands.

If your child is squirming, it may be hard to get an accurate reading. If so, remove the thermometer and use a different thermometer to take an oral, armpit, or forehead reading.

No-touch forehead thermometers usually have a removable cap that keeps it clean during storage. Make sure you take the cap off before use.

  1. Activate the device with the power button. You’ll know it’s on if it lights up and a startup sequence loads.
  2. When your thermometer is ready, position it no more than 2 inches away from the center of the forehead. You can also touch the forehead with some models. Either way, you’ll get the most accurate reading possible if the forehead is clean and clear of hair.
  3. Many thermometers have a guidance light that takes the guesswork out of positioning.
  4. Make sure to hold the thermometer steady. The thermometer and forehead must be free of movement in order to get an accurate reading.
  5. Press the temperature button.
  6. Your device will beep or flash to let you know the temperature is ready to be read. This will only take around 2 seconds.

Instructions for forehead thermometers vary by manufacturer, so make sure to read and hold onto the instructions or user’s manual that come with your device.

Digital thermometers are a popular option, which can be used orally, rectally, or under the armpit. There are some no-touch forehead thermometers that are also popular, especially in social settings.

In order to assess the thermometer reading accurately, follow the manufacturer’s directions.

Temperature readings vary, based on the type of thermometer you’re using.