At the top of the page, under DETAILS, in English there is a stat called "active" members (Japanese アクティブメンバー数) followed by a number.
At the bottom of the listing under GROUP PROFILE, there is a different number. In English this is also erroneously labeled "active" members. The Japanese version of the pages reads "Total" members (メンバー数).
Example: https://na.finalfantasyxiv.com/lodes...461.1593567535