What size filter do I need?

I've got the Nikon D5100 and I'm looking for some filters to use. I'm going to get the square filters so obviously ill need the adaptor ring. I'm using my 18-55mm lens… What size filter ring do I need to get?

Look on the front of your lens and it will tell you in mm --- maybe around 55mm filter it will say -- just guessing on that number.

Kit lenses for Nikon are 52mm.

To make sure, look closely at your lens for the diameter mark, denoted by a symbol that looks like this