The wikiFactor is calculated based on the ranking in the list of popular pages in any given MediaWiki based wiki. In this list the most visited page is ranked no. 1, the second most visited page no. 2 and so forth. Please note, that this is a purely quantitative measure. It does not say anything about how long a visitor was on that page, about the quality of the content of that page or if the visitor got anything at all from visiting that page. Just any page hit is counted, be it from human, search engine or other bot.
Now, based on the list of popular pages you can find the wF by comparing <the ranking number of that page, multiplied with 1.000> with <the number of "views" written right besides it>. The rank of the highest ranked page that still turns out to be higher in this comparison is the wikiFactor of that wiki.
For example a wikiFactor of, say, 10 means that page number 10 in the ranking of pages visited has received 10,000 or more visits, whereas page 11 has not yet reached 11,000 visits.