Throughout the stories of Chaos Warbands, there are some warbands which appear quite frequently. I was wondering how large chaos warbands are on average. I know it varies a great deal, some warbands are possibly the size of several space marine companies, some might be a dozen space marines or smaller. I know that some of the larger legions splintered a great deal (such as the World Eaters which basically fragmented into several howling bands).
I am guessing that in the Black Crusade setting, any group of characters is a "warband", even if it consists of 2 heritics and 2 Chaos Space marines. The book suggests that some of the larger warbands in the screaming vortex consist of thousads of heretecs, but some might be only a handful of followers around a charismatic leader.
As a reference, the books Soul Hunter and Blood Reaver state that the warband of Night Lords is approximately 50 Space Marines (though, this fluctuates during the book). Other Imperial armour books such as the Siege of Vraks suggest that warbands make an appearance but I am not too sure how large they are.
Any references in the books that shed light on this is appreciated.