What Is a Normal Body Temperature?

Body temperature is one of the four classic vital signs, yet there is considerably more nuance in what constitutes "normal" than the commonly cited 98.6°F (37°C) suggests. This figure, first calculated by German physician Carl Wunderlich in the 1850s, was based on millions of axillary measurements — and while it remains a useful reference point, modern research has refined our understanding of normal temperature ranges, individual variation, and the factors that affect readings.

The History Of 98.6°F

In 1851, Wunderlich measured axillary (underarm) temperatures in approximately 25,000 patients using a 30-centimeter thermometer that took 20 minutes to equilibrate. From these measurements, he calculated a mean temperature of approximately 98.6°F (37°C) and established the concept of a normal body temperature range.

This figure became embedded in medical tradition — but recent research suggests it may not perfectly reflect today's populations. A 2020 Stanford study analyzing temperature data from 677,000 measurements in 189,000 people collected over 157 years found that average human body temperature in the U.S. has declined approximately 0.05°F per decade since Wunderlich's time — meaning the average American's temperature today is closer to 97.5°F (36.4°C).