An adult dog's normal body temperature can range from 101 - 102.5° Fahrenheit (38.3 - 39.2° Celsius). A temperature of less than 99° F (37.2° C), or above 103.5° F (39.7° C), is considered to be dangerous and requires immediate veterinary care.
A 2014 study which compared axillary (armpit) temperatures with rectal temperatures in dogs and cats found a large gradient between the two, and concluded that, "axillary temperature should not be used as a substitute for rectal temperature."
Digital thermometers can be placed in a dog's armpit to provide an approximate body temperature, though axillary (armpit) temperatures are not considered to be as accurate as rectal or ear measurements.
Posted by Vuk Ignjic DVM on Monday, December 18, 2017
Measuring Body Temperature: Armpit Temperature for Anal Sac Disease