With present day materials and technology what is the physical size of a one milli Tesla magnet? How much "power" it has to attract pieces of iron? Please compare it with the objects we have around. What difference in size and "power" it gets each order of magnitude that I go up? What is a weak magnet what is a powerful magnet in this scale?
I would recommend you take a look at the K&J Magnetics website, particularly the magnet properties calculator: http://www.kjmagnetics.com/calculator.asp
Your question has too much ambiguity for a real answer, but I think that perhaps that page will address what you are wondering about.