This is a model that I have modified to hold 3" (7.5 cm) paper or you can change the dimensions to hold any square that you want. It is a self closing, one piece box. The original model is called Gift Box by Ms Shoko Aoyagi. I will explain how to measure the paper. The way I will teach the model is different than the diagram because of the modifications.
NOA #393 page 27
One sheet of 9 X 11 inch or 22.5 X 30 CM, scrapbook paper works well.
CM/Inch Ruler, pencil or pen
Small amount of measuring required