The best size for creating favorite icons is 16x16 pixels, which is the size at which they are most often displayed. However, they may sometimes appear in larger sizes (for example, 32x32 pixels). BY: university assignment writing - UK Academic Writers.
I use favicon size as recommended by the wp theme 512*512. It makes it square and sharp so that it is clearly visible and also readable But I saw a small favicon at university assignment writing! dont know the matter exactly