What is the difference between a small coil and big coil?

There are two main differences when using a smaller coil and a larger coil.  Small coils are better for trashier areas to get better target separation. You would use this in a park or an iron infested homesite. Small coils are also better to find small gold nuggets. Using a big coil give you more depth and cover more area. These coils are great for the beach and for fields.