(Source) 2020 BoysTown Folklore, Fun Facts, and Traditions from The Old Farmer’s Almanac
1897, scientist named Amos Dolbear published the article, The Cricket as a Thermometer that noted the correlation between the ambient temperature and the rate which rickets chirp.
Here is that formula…
To convert cricket chirps to degrees Fahrenheit, just count the number of chirps in 14 seconds, then add 40 to get the temperature.
It is said to be the approximation of the outside temperature.