What is the most common blade diameter for a portable circular saw?

The 7 1/4 inch saw has been the favourite size forever. However, I and many other pros switched to 8 1/4 about 20 years ago when DeWalt produced a great 8 1/4. I still use mine almost every day. I also have a 5 1/2 left hand Skil for smaller work. Both of these are very handy.