What are the Most Accurate Types of Thermometers for Taking a Person’s Temperature?

A thermometer is a measurement device used to take the range scale of temperature, such as the hotness or coldness of something. It can measure the temperature of different substances, like solids (food), liquids (water), or gas, such as air. It also detects changes in the physical properties of an object or substance as the object’s temperature changes. The three most common temperature measurement units are Celsius, Fahrenheit, and Kelvin.

The term thermometer came from two words, thermo (heat) and meter (measuring device). In household use, thermometers are utilized to see if you have a fever or tell you how cold it is outside. This type of tool has two critical elements for reading temperature gradient: temperature sensor and converting the sensor into a numerical scale. The sensor may include a mercury bulb in a glass form or a pyrometric sensor in infrared. This is where the indicator can be found if there is a change in the temperature. Meanwhile, the scale included the visible mark, which refers to the numerical value or equivalence. 

Brief History of Thermometer 

Doctor with Thermometer 

Human body temperature has been used as a diagnostic cue for health concerns since the beginning of clinical medicine. Greek physician Hippocrates considered that the human hand could be used to assess the presence of heat as early as 400 BC. Still, the instruments to measure this temperature were developed in the 16th and 17th centuries.

 In 1665, it was proposed to use the melting point of ice and the boiling point of water as references for standard temperature. The most commonly used scales today are the Fahrenheit, Celsius, and Kelvin scales. Since the dawn of medicine, medical professionals have accepted that the human body can exhibit an abnormal rise in temperature, commonly called fever, as a disease symptom.

The expansion and contraction of air with temperature changes were known as early as 220 BC by Philo of Byzantium. It was later found that water, like other liquids and metals such as mercury, has this property. As a result, many different thermometers have been developed today over hundreds of years. 

In 1868, Wunderlich established that the body temperature of a healthy person is constant, while in the case of illness, there are fluctuations in body temperature. The Allbutt thermometer was the first practical tool commercially available. Later, the technology improved and provided devices with high precision.

Types of Thermometers for Human Temperature 

The first thing to consider when using a temperature-measuring tool such as a thermometer is how you will use it. There are thermometers for infants and children and thermometers for adults. Then decide if you prefer mouth, ear, forehead, or no contact. Remember, many thermometers have multiple uses. 

The types of thermometers best used for human temperature; there are two general types:

Medical Devices  

1. Contact Thermometer

Touch/ contact thermometers need direct contact from the skin to gauge the temperature. The most common type of contact thermometer uses an electronic thermal sensor to detect body temperature. These thermometers can be used in different parts of the human body, such as the forehead, mouth, armpit, or rectum. Most electronic thermometers use a digital display that shows the temperature reading.

a. Digital Thermometer 

A digital thermometer works with a thermal sensor that measures your body temperature. They can read the temperature in the mouth, rectum, or armpit. When evaluating digital thermometer readings, be aware that armpit (underarm) temperatures are approximately 0.6°C (½ to 1°F) lower than oral readings. A rectal thermometer is hotter than an oral reading at 0.6°C (½ to 1°F). Digital thermometers offer precise readings in about 1 minute or less. 

b. Oral Thermometer 

Oral temperature can be measured with a digital thermometer or a mercury thermometer. The average mouth temperature is 37°C (98.6°F). However, mouth temperatures between 97°F (36.1°C) and 99°F (37.2°C) are considered standard. Oral thermometers are accurate in children over three and so as in adults. Some run naturally cool, while others run a little warmer. Knowing your average body temperature to determine if you have a fever when you feel sick is a good idea.

c. Digital Ear (Tympanic) Thermometer

Ear Thermometer   

A tympanic thermometer uses infrared technology to measure the temperature inside the ear canal. Tympanic readings are 0.5°F to 1°F higher than oral temperature readings. Tympanic thermometers provide quick and accurate readings and are preferred over oral or rectal thermometers, especially in children.

d. Forehead (temporal) Thermometer

Forehead Thermometer 

Forehead temperature readings are approximately 0.6°C (1°F) lower than oral temperature readings. A forehead thermometer uses an infrared sensor to measure the temperature of the external temporal artery, a carotid artery branch. 

e. Pacifier Thermometer

This type of thermometer is one of the easiest ways to record the approximate temperature of your baby or child. This is a type of thermometer that also acts as a pacifier. This thermometer must remain in the mouth, immovable, for up to 6 minutes. Additionally, they provide an approximate reading of temperature rather than an accurate reading.

2. Remote Thermometer

Many schools, businesses, and medical facilities screen visitors for fever, especially during the surge of Covid 19. Remote thermometers that do not require skin contact allow people to remain at a certain distance while the temperature is being measured. A remote thermometer can be used on the forehead (temporal artery) or the ear (tympanic membrane).

Most Accurate Thermometer for Human Temperature

The best thermometer is the most convenient and correct to use. It also helps if the thermometer is from a reputable manufacturer.

Medical Thermometer

Rectal temperature provides the most accurate reading for infants, especially infants under three months of age and children up to 3 years of age. Armpit temperatures are usually the least accurate. Oral readings are typically accurate for older children and adults as long as the thermometer is in place and the mouth is closed. For accurate readings when used orally, the tip of the device should be placed under the tongue with the mouth fully closed. For this reason, rectal measurements are considered the most accurate for infants.

Remember that your temperature readings will vary depending on how you used the device correctly.

If you need more information about buying thermometers, you can check out our Guide to Picking Thermometers for more tips and recommendations.

Thermometer Reading Tips


  • Rectal thermometer readings are around 0.5°F to 1°F higher than oral temperature readings.
  • Tympanic thermometer readings are typically 0.3°C (0.5°F) to 0.6°C (1°F) higher than oral temperature readings.
  • Temporal thermometer readings are often 0.5°F to 1°F lower than oral temperature readings.

Tips Before Taking a Thermometer Temperature Measurement

Oral Temperature

When taking a body temperature using the oral thermometer, wash your hands first and ensure your thermometer is clean and functioning. Turn the thermometer on and slip the plastic sheath over the bottom tip. The thermometer will show that it’s ready to be used with a sound or light signal. Place the thermometer’s tip underneath the tongue. Keep your mouth shut until you hear a sound. Remove the thermometer and read it. Wash your hands again and clean the device following the label’s instructions.

Rectal Temperature

It may be challenging to take a rectal temperature if your child is squirming, but this process offers more accurate temperature readings than the rest. So, to get started, wash your hands. Ensure that the thermometer is functioning. Cover the thermometer’s tip with a plastic sheath and apply lubricant, such as petroleum jelly. Babies can be placed on their backs, with their legs moving upward. 

digital thermometer

Turn on the thermometer and wait for its cue for use. Keep the thermometer straight; gently insert the tip into the rectum, no more than an inch. Hold it in place, preventing it from slipping out. Wait for a beep and remove the thermometer. Read the scale. Clean the device according to the manufacturer’s instructions and rewash your hands.


Measuring a person’s body temperature is integral to medical diagnosis and treatment. It is a rapid, non-invasive method of measuring a person’s temperature and can provide valuable information about their health status. Each process of taking temperature and the type of thermometer you will use predicts the accuracy of the temperature. For infants, it may sound like a handful of tasks, but there are several methods to make the process easier.