I use 2 builder's dumpy bags. Have just emptied 2010 vintage onto a border, last year's is breaking down well, so have empty bag for this year's lot. The leaves that fall in my garden are mostly beech. Ages ago, Gardening Which did a trial, and the most effective way to help the process was to shred leaves of possible (some garden vacs have a strummer thing built in), sprinkle on pelleted cluck muck as the layers are added and to keep it moist.