How Accurate are Thermometers?

You’ve probably heard that 98.6 degrees Fahrenheit is the healthy human temperature reading from a thermometer. But recent studies have suggested that is not the case. The reading of 98.6 came from a German physician who studied the recorded temperatures of about 25,000 people in the 1860s. However, a collection of twenty-seven recent studies on human temperature suggest that the average “normal” is lower, perhaps somewhere between 97- and 97.9-degrees Fahrenheit.See Disclosure ¹

The difference could be due to increased digital thermometer accuracy or to lower levels of underlying bacterial infection (and elevated temperatures) in the modern population. Whatever the case, scientists acknowledge there is a range of normal. This means that your personal current normal range may differ from your friend’s normal—or even what was your childhood normal.

In clinical terms, a fever is considered a temperature above 100.4 degrees Fahrenheit. Likewise, you are suffering from hypothermia if your temperature is 95 degrees Fahrenheit or lower. Therefore, don’t panic if your thermometer gives you a reading of 97.5 degrees Fahrenheit. It’s probably accurate, and your temperature is completely fine.

Digital thermometers are contact thermometers that read temperature through touch. They are the most common household medical thermometer. And like classic mercury-based thermometers, they can be used in various ways: for oral, armpit, aural (ear), or rectal readings. Keep in mind that a thermometer used for rectal readings should be reserved for that purpose alone.

With any contact thermometer, readings will vary depending on where the reading is taken. Oral readings are considered the standard, with other readings deviating above or below that. Armpit readings will run about half a degree to a degree lower than oral readings and rectal readings will read about half a degree to a full degree higher than oral readings.

Additionally, oral readings can be affected by eating or drinking hot or cold foods and beverages before taking your temperature. As such, it is best to wait 15 minutes after consuming anything before taking your temperature orally.

Both aural and temporal artery thermometers use infrared light (rather than contact) to read temperature. Some infrared thermometers, called aural or tympanic thermometers, take readings from the ear canal. Thermometer positioning and the presence of earwax can impact these readings, but when used properly and without disruption from debris, they can be quite accurate.

Additionally, many infrared thermometers are designed to read temperature from the superficial temporal artery that runs through the forehead. You’ve probably had your temperature taken this way in public settings as these thermometers have become popular since the onset of COVID-19.

However, keep in mind that sunlight, cold temperatures and sweat can interfere with the accuracy of these readings. Although, in general, accurate forehead thermometer readings run about one degree lower than oral temperature readings.

1. MacMillan, Carrie. “Is 98.6 Degrees Really a 'Normal' Temperature?” Yale Medicine. July 30, 2020. https://www.yalemedicine.org/news/temperature-checks-covid.

2. Mackowiak, Philip A. “The ‘Body Temperature’ Myth.” The American Journal of Medicine, Elsevier. November 6, 2022. https://www.amjmed.com/article/S0002-9343(22)00818-X/fulltext.