Not at all. In fact, there are many custom possibilities as to the size window and its position on the envelope. However, all window envelopes have one thing in common. The window needs to start at least 1/2" in from the left and 1/2" up from the bottom of the envelope. Even with all the custom window envelopes possible, there is still the traditional #10 Window Envelope. Here are its dimensions as well as templates to design off of Envelope Size: 4.125" x 9.5" Size of Window: 1.125" tall x 4.5" wide with 1/8" rounded corners Position of Window: 1.375" in from the left, 0.5" up from the bottom Templates: https://www.4over4.com/blank-templates/envelopes