The Farmer’s Almanac has the formula. But so do we, since we copied it from the Farmer’s Almanac, hoping and assuming that it is not copyrighted. Here it is:
To convert cricket chirps to degrees Fahrenheit, count number of chirps in 14 seconds then add 40 to get temperature.
Example: 30 chirps in 14 seconds + 40 = 70̊ F
To convert cricket chirps to degrees Celsius, count number of chirps in 25 seconds, divide by 3, then add 4 to get temperature.
Example: 48 chirps in 25 seconds/(divided by) 3 + 4 = 20̊ C
A couple of caveats: You have to isolate a single cricket. If 50 crickets are chirping and you count all of them, you’ll get an air temperature high enough to melt crickets. Secondly, it only works down to about 55 degrees Fahrenheit. Any colder and the crickets don’t chirp reliably. Male crickets do the chirping by rubbing their legs together. They establish territories and attract mates by chirping. It is a great sound unless it is echoing around your bedroom from the rafters above your bed and you are trying to sleep. For that you need a trained cricket-eating bird. Maybe a Greater Roadrunner.