Fine China

I have multiple plates from Normal Rockwell Collection there are 3 total which include the Spring-Spring Tonic, Summer-Cool Aid, and the Winter-New Year Look plates. All of these plates date back to 1978 and are all in original packaging include plastic covers, original boxes, and gold trimming with a detailed message on the back of the plate. I am not sure what size the plates are because I don't know how to measure diameter.