Lower case letters are average. How big should I write?

5cm x 5cm is too exaggerated. Just write in small letters as big as copybooks. At present, the photocopied version of the lower case copybook is basically the original font size (but the photocopied version of the running script often exceeds the original font size, and it is Wang Xizhi's Preface to the Lanting Pavilion, which often has an oversized version). I cut Wen Zhiming's original lower case with a machete in the preview of the Shanghai auction, and the size is about 6-7MM*6-7MM. But beginners learn lowercase letters, and once they write them, they become bigger. It takes a while to practice before they get smaller.