although it depends on the size of the legos, because they all
differ there is about roughly 180 regular sized LEGO pieces to each
single pound. but again it is hard to say because the variation in
lego piece size.
The average Lego weighs 2.5 grams per standard Lego of 2x4
studs. This means that six pounds contains 1090 standard 2*4 legos.
The actual amount will vary due to the different sized bricks.