There are three common rules for anchor chain length. In the first place, the anchor chain ought to be something like 15 feet long. Second, for normal conditions, there ought to be 1 foot of anchor chain per foot of boat length. Third for anchoring in cruel conditions or anchoring for the time being there ought to be 0ne foot of chain per six feet of anchor line. This implies that each 100 feet of anchor line ought to have around 17 feet of chain.