Before you purchase an anchor, look at what others are using in your area and ask other boaters.
The following is a Guide for the minimum size of a conventional 'Digging' type anchor (Plough, Fishermans, Bruce, Delta, CQR, Fortress, Guardian, ETC) for your vessel.
1KG is approximately equal to 2.2 pounds.
It is recommended that you carry 2 different types of anchor. A Main anchor, as well as a Secondary (used to be refered to as 'kedge') anchor. Also, it is adviceable to carry a folding grapnel anchor in any tender or dinghy.