If you are going to make a variety of bags and totes, visit a store (Target, Penney, etc) and try out different types of bags. Find a tote that you find very comfortable and measure the distance and the length of the straps. Do the same thing with a 'regular' handbag. Then you have a starting point. If you are short and you want to make a shoulder bag for a tall friend, add a couple inches to the length. I am 5'8" and when I make a messenger bag for a man, I add three inches and an adjustable clip so they could shorten it if they desired. I have found this has always worked.