class Book
include Mongoid::Document
field :name, type: String
end

Book.create name: 'fool'

Book.collection.stats

{"ns"=>"avatar.books", "count"=>1, "size"=>40, "avgObjSize"=>40.0, "storageSize"=>2304, "numExtents"=>1, "nindexes
"=>1, "lastExtentSize"=>2304, "paddingFactor"=>1.0, "flags"=>1, "totalIndexSize"=>8192, "indexSizes"=>

, "ok"=>1.0}