Every test on this site uses the same four formulas.
Gross WPM is all the characters you typed divided by five, divided by the elapsed minutes. Net WPM is gross WPM minus your uncorrected errors per minute, and it never goes below zero. Accuracy is your correct characters divided by your total typed characters, times one hundred. CPM is your correct characters divided by the elapsed minutes.
The five-character word is the standard convention used by typing tests since the typewriter era. It makes results comparable across different passages: a paragraph full of short words does not artificially inflate your score.
We also report consistency, which describes how steady your speed stayed from second to second. It is a descriptive statistic about one test, not a scientific measurement, and it is most useful for spotting whether you are typing in bursts.