Most box generators that you can find on the internet allow you to specify the size of the box. Sometimes you have to give inside measurements and sometimes outside measurements.
YAPPgenerator does this differently and starts from the printed circuit board for which you need a projectbox. The most important measurements are therefore the length, width and thickness of the printed circuit board. Then you specify where the holes are with which the printed circuit board should be secured. The holes can be used to secure the PCB with screws or you can clamp the PCB between the standoffs in the bottom and top of the projectbox. Then you can specify for all surfaces (lid, base, front, back, left and right) of the projectbox where rectangular and/or round cutouts should be placed.
Finally, texts can be entered that will be printed at the lid of the projectbox.