The size of the mugs I use are about 3 ¾ inches high and 3 to 3 ¼ in diameter. The orange one with the ties on this blog is the above size and it is a perfect fit. I often buy them at Goodwill. In the last few years, coffee mugs have become supersized.
If you plan to use an oversized mug, allow more room at the center fold lines and perhaps increase the same amount at the top fold line for the inner pockets.