The most recent poll of Iowa has Sanders 25%, Buttigieg 18%, Biden 17%, Warren 15%, and Klobuchar 8%. If that’s accurate, the caucus were held today, and the Iowa caucus were a primary rather than a caucus, that would mean that the top four candidates would receive those percentages of delegates and split the remaining delegates proportionally among themselves. The RCP Average of polls gives Biden a very slight lead.
But it’s a caucus and, due to the way it’s run, institutional and organizational support confers an edge. At this point I think that Sanders, Warren, and Buttigieg will fare slightly worse than their polling numbers suggest while Biden does slightly better. That could mean that Warren would be cut out entirely.