Nearly all the scholars of the Indian Subcontinent (with some notable exceptions) say it is wajib for a beard to be long enough for it to be entitely encompassed into your fist.
However scholars from the Middle East don't necessarily agree with this. The common view amongst them is that the beard needs to be of sufficient depth so that it is distinct from your jaw bone.
Our beloved Aqa and Mollah Salla Allahu ta'ala 'alayhi wa Sallam proclaimed "Trim closely the moustache, and let the beard flow (Grow)." - Narrated Ibn Umar Radi Allahu anhu in Muslim, Hadith no. 498
However to the best of my knowledge (and I am definitely not a scholar) there is no Hadith which specifies the exact length a beard should be.
The reason that Indo Pak scholars have stated that it neeeds to be a fistful is due to something that was done by Hadrat Abdullah ibn Umar Radi Allahu anhuDuring Haj Hadrat Abdullah ibn Umar Radi Allahu anhu cut "that portion (which exceeds the grip of the hand) of the beard." - Tirmidhi
Salafi and Wahabbis, as far I know, have taken a different intepretation on this. They believe that the beard should not be trimmed under any circumstances apart from when you are either in Haj or Umrah.That is why their beards tend to be longer heavier and more dense than most other groups of Muslims.
Deobandis on this issue share in the consensus that is prevalant in the sub-continent about beards needing to be a fist length.
One pominent Indian Sub-continent who deosn't share the consensus on this issue is Dr Tahir ul Qadri as far as I am aware he shares the Middle Eastern view on this issue.
What I have written is to the best of my knowledge if I have made any errors may Allah Subhanahu wa Ta'ala and my brother and sisters who have read this forgive me.